Individual 18650 capacity while still in Laptop battery shell?

KennyS

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I'm scavenging 18650's for an ebike build, and (unless anyone has a better suggestion) am getting the batteries from new laptop batteries as I come across them on ebay.
Problem is, as some of you know, some ebay sellers have a tendency to cheat when they feel they can get away with it. So my concern is buying batteries advertised as new but receiving used ones. The only way I'll be able to tell if they are used, or at least severely used is to check the capacity of the individual batteries once I get them out of the Laptop battery shell, so I need to know what the capacity should be.

For that reason, as well as knowing approximate individual 18650 capacity before I even buy the battery so I know what to buy or not to buy before hand, (looking for minimum 2000mAh capacities) I pretty well must have the formula to figure this.

We have the numbers on the assembled laptop batteries themselves, such as 8000mAh 4000mAh 5200mAh 4400mAh and so on to work with prior to buying and of course some LT batteries come with 6/9 or whatever individual 18650's batteries each, so I may also need to know how they are generally wired for any given amount of batteries, but I don't won't to get ahead of myself here. Hope there is a simple way as my knowledge on this stuff is limited. Can't seem to find the info anywhere so any help would be appreciated.

FWIW, I have something to calculate individual 18650 capacity.
 

Lynx_Arc

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Most laptop batteries are either one string or two parallel strings of cells. If it is one string then the capacity is (supposedly) what is listed either by number (mah) or by calculating watt/hours (Wh). As for the actual individual cell unless the batteries are weak/damaged etc then they should match what is listed, assuming that the manufacturer didn't exaggerate. I've scavenged 4-5 laptop battery packs and got 2000 and 2200mah cells, the 2600mah are less common as far as I've seen.
 

KennyS

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As for the actual individual cell unless the batteries are weak/damaged etc then they should match what is listed, assuming that the manufacturer didn't exaggerate.

Yes, the actual individual cell mAh, even before purchase is what I'm concerned about calculating. What you say about the Capacity of the batteries you scavenged might help some. It may be that we can assume most are 2000/2200 mAh. I'll look into that as it would help a lot if that's a fact and it does sound reasonable. Anyone here agree with 2000/2200 being average single battery capacity for laptop batteries?

Lynx, were the batteries you scavenged from new or used laptop batteries?

The only pack that I bought had 9 batteries, and the actual Laptop battery pack before I opened it up was 5800mAh 10.8V. It was supposed to be new, but the batteries tested with both a slow and fast test with 4 @ around 1950mAh, 1 in the 1600 range and 1750 or so for the rest. So I'm thinking it wasn't really new at all. Sound right to y'all? Or it could just be a cheap battery from a dishonest manufacturer and it is new. For $14.50, if they are new, I at least have some good flashlight batteries at a good price, but if they are nearing the end of their life cycle, not a good deal at all, and right off the top of my head, I'd say that is the case.

With the total capacity of unopened LT pack being 5800, how many mAh should each of my batteries have been?

Anyone know if one can tell by discharge and/or charge rate, that a battery is nearing death? Or if there is any "near death" test? Doesn't have to be right on, just need to get an idea.

Thanks, Lynx, that was helpful.
 
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Lynx_Arc

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As for the actual individual cell unless the batteries are weak/damaged etc then they should match what is listed, assuming that the manufacturer didn't exaggerate.

Yes, the actual individual cell mAh, even before purchase is what I'm concerned about calculating. What you say about the Capacity of the batteries you scavenged might help some. It may be that we can assume most are 2000/2200 mAh. I'll look into that as it would help a lot if that's a fact and it does sound reasonable. Anyone here agree with 2000/2200 being average single battery capacity for laptop batteries?

Lynx, were the batteries you scavenged from new or used laptop batteries?
I got them from name brand packs like HP, Dell, etc so I just assume that the specs are close to accurate as I don't have a battery analyzer to test them. These days I think that the 2000/2200 mah batteries should be commonplace such that unless you buy a cheap knock off battery you shouldn't have an issue.
The only pack that I bought had 9 batteries, and the actual Laptop battery pack before I opened it up was 5800mAh 10.8V. It was supposed to be new, but the batteries tested with both a slow and fast test with 4 @ around 1950mAh, 1 in the 1600 range and 1750 or so for the rest. So I'm thinking it wasn't really new at all. Sound right to y'all? Or it could just be a cheap battery from a dishonest manufacturer and it is new. For $14.50, if they are new, I at least have some good flashlight batteries at a good price, but if they are nearing the end of their life cycle, not a good deal at all, and right off the top of my head, I'd say that is the case.

With the total capacity of unopened LT pack being 5800, how many mAh should each of my batteries have been?

Anyone know if one can tell by discharge and/or charge rate, that a battery is nearing death? Or if there is any "near death" test? Doesn't have to be right on, just need to get an idea.

Thanks, Lynx, that was helpful.

9 batteries that equal 10.8v is three sets of parallel strings, that is you have 3P3S and 5800mah/3 is about 1900mah or so which falls within the range of 2000mah batteries it depends on if they test them and under what load they are tested. Under a lighter load they probably do put out 2000mah but as the load increases the capacity drops.

As for the charge/discharge rate and the health of lithium ion batteries as a battery loses capacity it should charge and discharge faster the only way to know is to measure the voltage while charging/discharging and having an idea what that correlates to charge condition or testing them by discharging them totally and recharging them fully. What I have seen in battery packs is either all the cells charge/discharge about the same rate or one set in the series loop charges and discharges faster and that usually includes self discharging which means if you let it sit for awhile and the batteries with lower capacity than the others tend to have higher internal resistance and in time the voltage will be noticeably lower than the others.
I would say if you want to test them and have stripped individual cells out of the pack put a heavy load on them (at least 1A) and time how long it takes them to drop in voltage to a safe discharge level. I'm not sure what that voltage would be I'm thinking about 3.4v should deplete them enough according to charts online.
If you aren't running cells in series but rather parallel then capacity differences shouldn't be a problem with runtimes related to the TOTAL capacity of all cells. It is best to have batteries with capacities in the same range when running in series to avoid damage to cells and possible hazards because of reverse charging and overheating.

There are others in the forum that know a LOT more about these batteries than I do, and there is a thread or two about scavenging batteries from laptop packs if you can find it probably will be worth gleaning over.
 

KennyS

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No good at math on paper but always seem to be able to figure it in my head somehow, and just after I posted I came up with the same figures as you did...these should be 1900 or so apiece. Also, this could still be a new battery and it's just cheap and the batteries were mismatched in capacity. I say that because it would seem they'd all go down if it were used a lot but they didn't, some are higher and some are lower and the higher ones are still at expected capacity.

Got the 4 18mAh SLA batteries in today, just something to get me going on the bike for now and use as a small emergency power bank when I finish the 1860 battery build, but those things are heavy, like 40 something lbs, so the 18650 pack is going to be a must.

You gave me a lot to work with here in testing and I will use it, as well as check for other threads. Yes, others may know more but your willingness to go to the trouble is what I have and much appreciated. I may report back if I have anything to add or when I get all my batteries together and have questions. Thanks again for a very helpful reply, Lynx.
 

Lynx_Arc

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No good at math on paper but always seem to be able to figure it in my head somehow, and just after I posted I came up with the same figures as you did...these should be 1900 or so apiece. Also, this could still be a new battery and it's just cheap and the batteries were mismatched in capacity. I say that because it would seem they'd all go down if it were used a lot but they didn't, some are higher and some are lower and the higher ones are still at expected capacity.
There can be variations in voltage but typically under light loads they should charge up to and discharge to within about 0.1v of each other, under heavier loads this could vary a little more perhaps 0.2-0.4v or so. I'm thinking as batteries are under a heavy load in a pack some get hotter than others due to thermal conduction.
Got the 4 18mAh SLA batteries in today, just something to get me going on the bike for now and use as a small emergency power bank when I finish the 1860 battery build, but those things are heavy, like 40 something lbs, so the 18650 pack is going to be a must.
I'm guessing that is a typo and you met 18Ah not mAh and SLAs are nice but rather heavy and to me seem to die too fast for the price IMO.
You gave me a lot to work with here in testing and I will use it, as well as check for other threads. Yes, others may know more but your willingness to go to the trouble is what I have and much appreciated. I may report back if I have anything to add or when I get all my batteries together and have questions. Thanks again for a very helpful reply, Lynx.
I'm still myself tinkering with 18650 cells... I've pulled them out of bad drill packs even to use in projects buying cheap power bank shells but most of the drill batteries are lower capacity perhaps 1000-1500mah as I'm guessing the lower capacity makes for lower internal resistance and higher current with more cycles than higher capacity batteries would give. If I could find a bunch of cheap laptop batteries of 2600mah or so that would be nice but they tend to cost about twice as much as the 2000-2200 ones do. If you are tinkering a lot and have the funds an investment into a lithium battery charger with analyzer would be good that way you can match them better and weed out the weaker ones easier.
 

hellokitty[hk]

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Look for voltage specs for figuring out how many are in series.
Then you can divide and get one or two good guesses for how many in parallel, as you said, for example ~2000mAh is fairly common for many older laptops.
Some newer nicer laptops can potentially have ~3000+ mAh batteries; but those will be fairly expensive. Try to look up the price of a replacement batterypack. A nice pack with cells like 2900mAh will probably cost about $10 per cell, from a normal retailer.

It should be possible to figure out exactly without too much difficulty. The spread between a low capacity cell and a high capacity cell is small enough that most of the time, you will only have one legitimate possibility.

One last trick is to physically look at the size of the packs. It's pretty common to see a pack with 3-4 in series (length), and you will see that the width of the pack is approximately two batteries across. then you know your answer.
 

Lynx_Arc

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Look for voltage specs for figuring out how many are in series.
Then you can divide and get one or two good guesses for how many in parallel, as you said, for example ~2000mAh is fairly common for many older laptops.
Some newer nicer laptops can potentially have ~3000+ mAh batteries; but those will be fairly expensive. Try to look up the price of a replacement batterypack. A nice pack with cells like 2900mAh will probably cost about $10 per cell, from a normal retailer.

It should be possible to figure out exactly without too much difficulty. The spread between a low capacity cell and a high capacity cell is small enough that most of the time, you will only have one legitimate possibility.

One last trick is to physically look at the size of the packs. It's pretty common to see a pack with 3-4 in series (length), and you will see that the width of the pack is approximately two batteries across. then you know your answer.
There are many packs that don't even list mah specs that I've seen, instead they list Wh like.... 64Wh. With these packs you first divide the Wh by the voltage of the pack listed that will give you Ah and multiply that by 1000 for mAh.
I've looked some on ebay for the ~3000mah laptop battery packs and they start around 33.00 at that price you either need to really know what you are getting or just order single cells from reputable dealers instead.
 

KennyS

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There are many packs that don't even list mah specs that I've seen, instead they list Wh like.... 64Wh. With these packs you first divide the Wh by the voltage of the pack listed that will give you Ah and multiply that by 1000 for mAh.
I've looked some on ebay for the ~3000mah laptop battery packs and they start around 33.00 at that price you either need to really know what you are getting or just order single cells from reputable dealers instead.

Thanks to you both. Lots of real good stuff from y'all along with what I pick up by doing, is going to help a lot. I can see this is going to be a take it as it comes thing and as you both indicate there will be guesses then choosing the best guess, at least on trying to figure things before I actually get the batteries in hand. I did notice the size variance from almost square to rectangle.

Seems I paid about twice what I maybe should have for the first pack and many of these are going for around $6 while I paid $14.50 for the first pack. I did a buy it now on the first as I hate waiting for auctions, but auctions seems to be to be the way to go. Just paying the slightest bit of attention to what one is doing will produce some good deals, right on up to great deals after a learning curve. I did get my second pack in today, a BIN @ around $14.50, and I'm thinking I must have paid better attention to brand. I'm charging now to get a capacity but they all seem very even, and turns out they were all marked as actual Samsungs. Though I was unable to find the ID in a search for the first batch (probably a bad sign), this batch, ICR 18650-26f showed right up, and not tested yet but appear to be good, brand new 2600's. They are charging evenly and had pretty good voltage right out of the pack so, we'll see. May have paid to much, maybe not for these 9, but new Samsung 2600's for a buck and a half each... ain't bad at all.

On ripping these apart, since I may be doing a lot of them...any tips? The first was nothing, cracked at the seam and was piece of cake. The second, I got the front seam but had to dremel around it to pop the rest of it open, not something I like doing. I didn't go all the way through for the most part...but the potential for damage still looms close with that method. And maybe a few tips on what to expect on pricing from your hands on experience would be helpful too.

No problem with a few muck ups or bad deal as I get started here and hopefully I'll get better at this as I go on and get the first build behind me. Got the bike conversion kit in today so didn't take time to retest the first batch as there are all kinds of thing for me to play with now, but I will. If this goes OK, and I don't absolutely love this bike but like the idea of it, I may sell it, hopefully for a little profit and go with a fat bike,and that should get rid of the SLA's and maybe I'll be well into getting the 18650 pack done by then.

I'm not ready for this yet and am not really up on what my options are concerning Parallel/Series, but I might as well get this out there. As I understand it, I need 72/18650's fro a 48 volt set up...correct? I've watched some of the youtube videos but am still a little in the dark about the wiring/balancer/charger and what not (hey, at least the SLA;s are simple). I guess that's mostly because I don't want to clutter my mind with too much at once. I should be able to find a good tutorial on that when I get down to it. Anything you might want to touch on in that area, just in general or whatever would be helpful. I did have one question in particular...I see we can buy the plastic holders to make a nice neat pack or it will be a little more compact if just taped and shrink wrapped. The question is about heat, and would it be better to use the holder as it appears to leave space between the batteries, as opposed to the batteries going right up against each other...or is heat damage over time a real factor here?

Thanks again and any more ideas...well keep em coming.
 
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Lynx_Arc

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Seems I paid about twice what I maybe should have for the first pack and many of these are going for around $6 while I paid $14.50 for the first pack. I did a buy it now on the first as I hate waiting for auctions, but auctions seems to be to be the way to go. Just paying the slightest bit of attention to what one is doing will produce some good deals, right on up to great deals after a learning curve. I did get my second pack in today, a BIN @ around $14.50, and I'm thinking I must have paid better attention to brand. I'm charging now to get a capacity but they all seem very even, and turns out they were all marked as actual Samsungs. Though I was unable to find the ID in a search for the first batch (probably a bad sign), this batch, ICR 18650-26f showed right up, and not tested yet but appear to be good, brand new 2600's. They are charging evenly and had pretty good voltage right out of the pack so, we'll see. May have paid to much, maybe not for these 9, but new Samsung 2600's for a buck and a half each... ain't bad at all.
I'm not sure not being able to look up markings is a bad thing or not as some markings are the batch number and have nothing to do with capacity at all I have some I pulled from a pack that turn up nothing that are out of a 2200mah pack. It is better to get known brand names and see obvious markings to the capacity for sure if you are looking for higher capacity cells like 2600 and up but for the lower stuff I'm guessing you should get them under $2 a cell and 2000/2200 is ok. I picked up a few 1300 and 1500s out of drill packs myself to use for tinkering and I have a handful of USB led lights that I plug into cheap power banks to tinker with.
On ripping these apart, since I may be doing a lot of them...any tips? The first was nothing, cracked at the seam and was piece of cake. The second, I got the front seam but had to dremel around it to pop the rest of it open, not something I like doing. I didn't go all the way through for the most part...but the potential for damage still looms close with that method. And maybe a few tips on what to expect on pricing from your hands on experience would be helpful too.
I tend to use two flat blade screwdrivers myself one to hold the open seam and the other to pry it open even more where it is barely able to get in the crack. I saw a youtube where a guy took a hammer and smacked the seams of a set all around in about 10 seconds and pulled the plastic shell right off..... looked too easy but I guess if you have a dozen to do you could get to where you could do this way safely with that much practice. The hardest thing I've found is getting the adhesive off the batteries. You need something like a plastic scraper I've used a guitar pick and I have a dremel to clean up the tack joints after the welds are pulled off.
No problem with a few muck ups or bad deal as I get started here and hopefully I'll get better at this as I go on and get the first build behind me. Got the bike conversion kit in today so didn't take time to retest the first batch as there are all kinds of thing for me to play with now, but I will. If this goes OK, and I don't absolutely love this bike but like the idea of it, I may sell it, hopefully for a little profit and go with a fat bike,and that should get rid of the SLA's and maybe I'll be well into getting the 18650 pack done by then.

I'm not ready for this yet and am not really up on what my options are concerning Parallel/Series, but I might as well get this out there. As I understand it, I need 72/18650's fro a 48 volt set up...correct? I've watched some of the youtube videos but am still a little in the dark about the wiring/balancer/charger and what not (hey, at least the SLA;s are simple). I guess that's mostly because I don't want to clutter my mind with too much at once. I should be able to find a good tutorial on that when I get down to it. Anything you might want to touch on in that area, just in general or whatever would be helpful. I did have one question in particular...I see we can buy the plastic holders to make a nice neat pack or it will be a little more compact if just taped and shrink wrapped. The question is about heat, and would it be better to use the holder as it appears to leave space between the batteries, as opposed to the batteries going right up against each other...or is heat damage over time a real factor here?

Thanks again and any more ideas...well keep em coming.
My advice is to label batteries that don't have obvious writing on them attesting to their capacity and to keep batches together of batteries from like cells especially capacities. I'm not sure what setup you need so many batteries for but I'm thinking that that link m41ausr posted may turn out better for you if you figure cost per cell per mah a 3400mah cell has about 30% more capacity that would make for having to deal with fewer batteries in the long run. If you are going to put a lot of cells together you may want to consider investing in a welder or making yourself one and buying some metal to weld. As for the heat it depends on how much current is being run through the average battery if the current is low enough heat shouldn't be an issue but if it gets too high then it can cause the hotter batteries to discharge perhaps faster and wear them out quicker even perhaps ruining them if they reverse somehow.
 

KennyS

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Thanks, M4, would love to have 3400's but though they are a higher capacity, and at a good price indeed, for my budget they may not work, but maybe after all is considered.

I guess it was stated but I never could find just how many were in a cluster?
 

KennyS

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I'm not sure not being able to look up markings is a bad thing or not as some markings are the batch number and have nothing to do with capacity at all I have some I pulled from a pack that turn up nothing that are out of a 2200mah pack. It is better to get known brand names and see obvious markings to the capacity for sure if you are looking for higher capacity cells like 2600 and up but for the lower stuff I'm guessing you should get them under $2 a cell and 2000/2200 is ok. I picked up a few 1300 and 1500s out of drill packs myself to use for tinkering and I have a handful of USB led lights that I plug into cheap power banks to tinker with.

Yeah, I agree...I'm looking for brand names now. With the two batches i got, it was a crap shoot as they were both advertised as replacements and nothing on the packaging indicated other wise. The first, I'm retesting and they may be OK at best unless they are steadily losing capacity with each charge, and I am marking them. The second were all fine, almost. From 2504 to 2591. Seems like good new 2600's however 1 was dead. so Id guess the guy bought it as new and it was but defective and figured he'd just get the customer to test it for him, at least in a sense. So he essentially sold me a bad laptop battery that wouldn't have done jack for a laptop, but for the price ir worked out very well. I've got some auctions marked to bid and we'll see how that goes.

I tend to use two flat blade screwdrivers myself one to hold the open seam and the other to pry it open even more where it is barely able to get in the crack. I saw a youtube where a guy took a hammer and smacked the seams of a set all around in about 10 seconds and pulled the plastic shell right off..... looked too easy but I guess if you have a dozen to do you could get to where you could do this way safely with that much practice. The hardest thing I've found is getting the adhesive off the batteries. You need something like a plastic scraper I've used a guitar pick and I have a dremel to clean up the tack joints after the welds are pulled off.

Yes, two or more screwdrivers and since you mentioned guitar picks, just recalled I have seen then use several of those to pry the glass from cell phones for replacement. IOW if you have them like I do, good spacers and never considered it but beats my finger nail for scraping. I like the hammer trick and will look into it. There ya go, got the dremel and never considered it for the tack joints. I have a few flashlights and some Vaping mods I was having to use a tiny magnet to get the positive connection to work with flat tops, but have found, leaving the tack in place solved that. Don't really like a magnet freely floating around in anything but especially an expensive box mod. Nope, never even though to solder the positive tops as a spacer, sometimes the obvious just slips by.

My advice is to label batteries that don't have obvious writing on them attesting to their capacity and to keep batches together of batteries from like cells especially capacities. I'm not sure what setup you need so many batteries for but I'm thinking that that link m41ausr posted may turn out better for you if you figure cost per cell per mah a 3400mah cell has about 30% more capacity that would make for having to deal with fewer batteries in the long run. If you are going to put a lot of cells together you may want to consider investing in a welder or making yourself one and buying some metal to weld. As for the heat it depends on how much current is being run through the average battery if the current is low enough heat shouldn't be an issue but if it gets too high then it can cause the hotter batteries to discharge perhaps faster and wear them out quicker even perhaps ruining them if they reverse somehow.

On the 3400 deal M4 posted, wish I were more ready and knew what I needed for the 48v system. See I think the guy on youtube was getting something like 100 mi from his 72cell packs, a phenomenal range and I really don't need that but don't know yet how to figure a 48v pack with less batteries so, I'll just stick with what I'm getting for now, can always use them but should go ahead and look in what I need now if I can do the figures. If not maybe once I get it figured out he'll still have some left. It may well be worth going that route in time saved, guaranteed new, as well as weight/space savings from higher capacity batteries. On putting them together, I was just going to so solder but I have a mini mig welder and just remembered that. I never use it because I can't weld except to make an embarrassing blob that will do the job on occasion. Wire about the width of a paper clip? or something like that...would a mig like that even be useful? Best I can gather the battery heat is not an issue but thanks for verifying and for all the other advice.
 

Lynx_Arc

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I'm not sure about a mig welder for battery packs maybe someone else could advise you on that. As for the magnets some people have said they super glue them around the edges in place I think I saw a button top for batteries but you may have to rewrap them.
 

KennyS

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I'm not sure about a mig welder for battery packs maybe someone else could advise you on that. As for the magnets some people have said they super glue them around the edges in place I think I saw a button top for batteries but you may have to rewrap them.

It's a tiny little wire feed, and I think I can turn the voltage down to pretty weak. The more I think about it, it could be just the thing..maybe wire type is the key there. I'll look into it or just try it. If I don't come back, maybe things didn't go too well. :)
 

Lynx_Arc

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It's a tiny little wire feed, and I think I can turn the voltage down to pretty weak. The more I think about it, it could be just the thing..maybe wire type is the key there. I'll look into it or just try it. If I don't come back, maybe things didn't go too well. :)

Just make sure you have a bucket of sand or something near by just in case of fire. I'm not really sure turning the voltage down will but make things worse I'm thinking that quicker you get it done the less heat is transferred into the battery chemicals. It may be you can drill a few holes in the metal strap you are welding and weld the hole shut to the battery top/bottom. I would have to hope someone with more experience with mig welders than I have chimes in here. I've used a mig but on 1/4 inch and thicker metals nothing thin like this.
 

KennyS

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On the voltage, it'll be touch and go. I'd guess you are right and there is a point where too low voltage could cause a problem. Kind of like a lower power solder iron can actually make things hotter. That's a good idea on the holes...I can see how, if it doesn't work normally, that could very possibly make it happen.

I tried to put the SLA batteries on the bike rack and the bike won't even stand by itself so, way too much weight. Fortunately it works fine installing them in the trailer which I needed anyway. Won't hurt to have both sets of batteries for when I need the trailer and when I just want to joy ride. Thanks for the advice.
 
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