# Led Lenser P7 with Rechargeable Batteries question



## Lampie (Jan 12, 2009)

In a couple of days I'll recieve my first "pro" flashlight, the Led Lenser P7. I'm going to use the P7 for biking. The P7 will have to stay on high mode for 60 - 90 minutes.

I have 8 Sanyo Eneloop AAA NiMH Rechargeable Batteries (800 mAh) and I was wondering if I could use these. I emailed Led Lenser (zweibrueder), this is the reply they've send me:



> please use only alkaline Batteries in our products. All other batteries also lithium and accu cells can damage the electronic or the LED.


Should I not use these Eneloops and go for alkaline batteries? I've read that some members here do use Eneloops in their Led Lenser but I don't know for how long. Will the Eneloops damage the P7 when operating on high mode for 60 - 90 minutes?


----------



## Kilovolt (Jan 12, 2009)

I got the same answer from Zweibrueder a couple of months ago when I bought my P7 and asked the question.
The fact is that apparently their technicians took into account the quick drop of voltage of alkaline batteries in the thermal design of these lights. NiMH's on the contrary keep their 1.2V practically constant for the whole duration of their charge. 

I normally use 850 mAh Energizer NiMH cells in my P7 but my use is limited to a few minutes each time and I kept it on for 90 minutes only once or twice to check the runtime. In your case can't you switch the P7 to low for a few minutes from time to time to let it cool down a bit? In the affirmative I would feel safe with the rechargeables.


BTW: welcome to CPF!


----------



## Marduke (Jan 12, 2009)

The P7 is a direct drive, resistor based light that accounts for the initial voltage drop and higher internal resistance of alkaline cells. Because of that, prolonged use of NiMH cells carries the possibility of overheating. Many people do it and get away with it, but the inherent design characteristics tend to make such flashlights (direct driver, resistored, multiple AAA configs) unpopular with many CPF members.

:welcome:


----------



## Lampie (Jan 13, 2009)

Kilovolt said:


> In your case can't you switch the P7 to low for a few minutes from time to time to let it cool down a bit? In the affirmative I would feel safe with the rechargeables.



I could do that but I would have to stop because it's to dark to see the road.

How long will the P7 run in high mode with 4 alkaline batteries?



Marduke said:


> Many people do it and get away with it



For more then 60 minutes continuasly? (great explanation :thumbsup

Thanks for the "warm"  welcome!


----------



## Gunner12 (Jan 13, 2009)

The LedLenser seems to depend on the drop of voltage of the alkaline AAA, when they are being punished through high current, to keep the heat from the LED in a manageable for the relatively small pedestal which the LED sits on to transfer heat from the LED to the body of the light(ok, that was on long and complicated sentence, pretty much what Marduke said). Rechargeable batteries hold their voltage much better then alkaline batteries espicially at that current. Higher voltage = higher current = more power to the LED, which could mean too much heat. It should be ok though.

You might be able to test by turning on the light and seeing how long it takes to get warm. If it's a relatively short time, then you should be fine. If the light never gets warm, then no, don't use rechargeable batteries.

:welcome:


----------



## herrgurka (Jan 13, 2009)

I bought a Lenser P7 in my pre-CPF days and have been using it with Eneloops since day one. It doesn't see too much action nowadays, to heavy for EDC, but I do use it as a workhorse around the house. Until now I haven't had any problems due to heat (e.g. tint changes). It does get warm after 20 minutes on high but the temperature stays well below some of my Jetbeams for example. The same goes for the - admittetly rather measly - heatsink.


----------



## Holepuncher (Jan 13, 2009)

I tested mine with NiMH and measured the current into the LED at 1.4A on turbo mode or whatever they call it. Due to the way this light is constructed, and the difficulty in getting an access point to measure (without unsoldering the led) I had to use small gauge alligator clip leads to make this measurement. These leads could easily have introduced several 1/10 of ohms making the 1.4 amps reading a little lower than it should be. So I'll state it as a minimum of 1.4 amps. Whether or not the Cree can withstand that I'll leave to the experts here but you will only get 30 minutes of run time with your 800 mah batterys so you dont have to worry about 90 minutes.


----------



## Swedpat (Jan 13, 2009)

I become more and more irritated about how LedLenser deceive their customers. Announcing a brightness level as a selling argument when that level it isn't aimed to be used. 
*Or am I wrong*, is the max brightness higher than stated the very first minutes of the runtime with 1,5V alkalines?
Anyway it's a bad construction if it cannot be used with 1,2V NiMh batteries. In my opinion...

Regards, Patric


----------



## kramer5150 (Jan 14, 2009)

Swedpat said:


> I become more and more irritated about how LedLenser deceive their customers. Announcing a brightness level as a selling argument when that level it isn't aimed to be used.
> *Or am I wrong*, is the max brightness higher than stated the very first minutes of the runtime with 1,5V alkalines?
> Anyway it's a bad construction if it cannot be used with 1,2V NiMh batteries. In my opinion...
> 
> Regards, Patric



I don't think its deceitful... its more a "partial truth". many manufacturers are guilty of quoting output and runtime specs without specifying all the relevant parameters with which to accurately judge the product. But thats why we have CPF... to expose the truth.

You should also be aware that ANY direct drive 3AAA light will perform exactly as you describe, because their output characteristics are directly dependent on the type/quality of cells used.


----------



## Kilovolt (Jan 14, 2009)

Swedpat said:


> I become more and more irritated about how LedLenser deceive their customers. Announcing a brightness level as a selling argument when that level it isn't aimed to be used.
> *Or am I wrong*, is the max brightness higher than stated the very first minutes of the runtime with 1,5V alkalines?
> Anyway it's a bad construction if it cannot be used with 1,2V NiMh batteries. In my opinion...
> 
> Regards, Patric


 

I become more and more irritated by the fact that any discussion on this subject in the Forum becomes an opportunity for a LEDLenser bashing spree. :shakehead

I would kindly ask those who hate LL products to abstain from participating in threads concerning a specific technical issue by adding posts on how badly these lights are designed, etc. :devil:


As to what Holepuncher has measured I would like to add that it is unrealistic that anyone keeps the switch pressed for 30 minutes or so to achieve the turbo mode and therefore a correct current reading should be based on the high level.

This is what I get at high level in my P7 with 4 x 800 mAh NiMH's







I would say about 95 minutes to 50% plus a 'useful amount of light' for another 10-15 minutes. Based on this I think that the actual current can't be much more than 500 mA.


----------



## Egsise (Jan 14, 2009)

Very similar results can be found in here.
There is also nice comparison between Led Lenser P7 and regulated lights.


----------



## DM51 (Jan 14, 2009)

Swedpat said:


> *I become* *more and more irritated* *about how LedLenser* *deceive their customers*. Announcing a brightness level as a selling argument when that level it isn't aimed to be used.
> Or am I wrong, is the max brightness higher than stated the very first minutes of the runtime with 1,5V alkalines?
> Anyway it's a bad construction if it cannot be used with 1,2V NiMh batteries. In my opinion...


There are reasonable ways of making a point (if it is essential that it be made) and then on the other hand there is the way you have done it here. You have jumped into this thread with a trollish post, and you can plainly see the result - however irritated you think _you_ may be, others have been far more irritated by your entirely superfluous post. That is essentially what trolling is - starting unnecessary trouble where there was none before. If you do it again, your account will be suspended.


----------



## defloyd77 (Jan 14, 2009)

The thing to keep in mind though, is Lampie will be using it for biking, so I think that there's even less concern with heat. Little off topic but do you think using nimh in the 1aaa P3 would also have the same concerns of being driven too hard for too long?


----------



## Holepuncher (Jan 14, 2009)

Kilovolt said:


> I
> 
> As to what Holepuncher has measured I would like to add that it is unrealistic that anyone keeps the switch pressed for 30 minutes or so to achieve the turbo mode and therefore a correct current reading should be based on the high level.
> 
> ...




I did measure the current at the high level. I should have posted it but I thought the OP's concern would be if it fried on the turbo mode. I measured approx 700 ma with both NiMH (hot off the charger) and alkalines. It would seem your curve is spot on because the hot off the charger reading would be a little high and would probably drop off to around the 500mA you mentioned. If anyone is interested I will run a complete discharge curve. The only thing is due to the way the light is constructed, would it count if I took the battery pack out of the light and connected it to a star mounted CRE XRE on the bench?

While correct, Your statement of 95 minutes to 50% does not do it justice. Looking at the curve, 1.25 hours of nearly full output sounds better. There is probably less than 10% drop in output over that range. Hardly enough to notice in actual use.


----------



## Kilovolt (Jan 14, 2009)

defloyd77 said:


> Little off topic but do you think using nimh in the 1aaa P3 would also have the same concerns of being driven too hard for too long?


 
Together with the P7 I got a free P3 from the UK dealer. 

The P3 instruction sheet bears the same sentence as the P7's one concerning the use of rechargeables: not allowed.
But the P3 does not have a CREE LED but a Nichia. Personally I can't believe that this LED could be damaged by a constant 1.2V voltage so I would feel safe using a NiMH.



Holepuncher: thanks for the info on the current. :thumbsup:


----------



## Egsise (Jan 14, 2009)

Holepuncher said:


> While correct, Your statement of 95 minutes to 50% does not do it justice. Looking at the curve, *1.25 hours of nearly full output sounds better*. There is probably less than 10% drop in output over that range. Hardly enough to notice in actual use.



"nearly full....sounds better...." :huh:

Runtime from 100% to 50% output is widely used and way better imho, it is easier to compare runtimes of different lights when there are numbers involved. 
Rather than "nearly full output ", "enough useable light", "max 100lum and 100h runtime" or some other better sounding phrase.

And actually Led Lensers get better results that way, compared to regulated flashlights that have nearly full output much longer and dim in a few minutes.


----------



## Ragiska (Jan 14, 2009)

Kilovolt said:


> I become more and more irritated by the fact that any discussion on this subject in the Forum becomes an opportunity for a LEDLenser bashing spree. :shakehead
> 
> I would kindly ask those who hate LL products to abstain from participating in threads concerning a specific technical issue by adding posts on how badly these lights are designed, etc. :devil:
> 
> ...



but lenser says specifically to not use nimh cells. can you do a runtime on alkaline cells?


----------



## Holepuncher (Jan 14, 2009)

Ragiska said:


> but lenser says specifically to not use nimh cells. can you do a runtime on alkaline cells?



Lets clarify this issue. On the low and high setting there would be little difference in output and drive current when using either NiMH or Alkaline. The only concern would be in the turbo mode and as kilovolt mentioned it would be unlikely that anyone would keep the switch pressed for any length of time. And there is really no need to. There is simply not a dramatic difference in brightness between high and turbo.


----------



## Kilovolt (Jan 14, 2009)

Ragiska said:


> but lenser says specifically to not use nimh cells. can you do a runtime on alkaline cells?


 
It has already been done by a member of the MesserForum, please check the link mentioned by *Egsise*.


----------



## Kilovolt (Jan 14, 2009)

Holepuncher said:


> Lets clarify this issue. On the low and high setting there would be little difference in output and drive current when using either NiMH or Alkaline. The only concern would be in the turbo mode and as kilovolt mentioned it would be unlikely that anyone would keep the switch pressed for any length of time. And there is really no need to. There is simply not a dramatic difference in brightness between high and turbo.


 
Holepuncher, if you compare the red and green lines relevant respectively to NiMH and alkaline batteries in the MesserForum runtime test you can clearly see how much less stressed the LED is with the latter. It has more or less clearly been stated by LL designers that they count on that difference to ensure a long life to the LED itself.


----------



## Holepuncher (Jan 14, 2009)

Kilovolt said:


> Holepuncher, if you compare the red and green lines relevant respectively to NiMH and alkaline batteries in the MesserForum runtime test you can clearly see how much less stressed the LED is with the latter. It has more or less clearly been stated by LL designers that they count on that difference to ensure a long life to the LED itself.



I see what you mean. There is about a 20% difference in stress. As I mentioned in one of my earlier posts I measured about 700 ma for both NiMH and Alkaline and thats what I based my comment on. The "0" point of the red and green lines in the curves confirm my measurement. It looks like there is a 15% or so drop in the first 5 minutes for both the red and green. With proper heat sinking the Cree is rated for 1000mA. This light may not have proper heatsinking but there is a decent chunk of metal under the led - probably enough to handle 600mA or so continuously. We are not talking about over stressing here. On turbo that may be entirely different. A quick measurement I did yesterday showed 1200mA with fresh alkalines on turbo so even with alkalines the light can be over stressed.


----------



## LED_Thrift (Jan 14, 2009)

Welcome to CPF Lampie. As defloyd77 mentioned, since you will be using it for biking, there will be additional cooling [especially this time of year where I live - brrr 14F now] while you are moving. As also was suggested, if you would turn the light down to medium [maybe while also using your backup light], there would be a lot less chance of a problem. 

If I had a light for dedicated to bike usage, I would consider soldering on a few cooling fins on the part of the light that gets warmest.


----------



## Holepuncher (Jan 14, 2009)

If anyone is interested the resistors used in this light are 1.5 Ohms for the high mode and 100 Ohms for low.

In the high mode (without actually having a complete discharge curve) if we assume my measured value of 700 mA we are wasting about 0.7 watts in the resistor. At 700 mA we should be around 2.5 watts into the LED. This would give an efficiency of around 75%. Not to bad. 

In the low mode, we won't concern with efficiency, but assuming a battery voltage of 6 volts and an LED forward voltage of 3 volts meaning 3 volts are dropped in the resistor giving a Low mode current of around 30 mA. Assuming 800 mah batterys the runtime on low should be 25+ hours


----------



## Fallingwater (Jan 15, 2009)

You could swap the high-mode resistor with a slightly more restrictive one and use NiMH cells with no problems.


----------



## yellow (Jan 15, 2009)

defloyd77 said:


> The thing to keep in mind though, is Lampie will be using it for biking, so I think that there's even less concern with heat.


thats it! 
Heat is no problem!
A light that gets hot, does not even show the slightest heat when mounted on the bars.
No additional fins or such needed
(I am doing this for 1.5 years now, even lights that overheat at testing without forced air from a fan show almost no heat, when they have a metal body)


Your primary problem (except for the Lenser itself)  is the 3 AAA battery - unsuitable and bad.

Get a good regulated 2 AA flashlight, or - better - one that is driven from an 18650 Li-Ion


PS: I like the graph Kilovolt has posted and would have bet on a much inferior from that light


----------



## SureAddicted (Jan 15, 2009)

yellow said:


> Your primary problem (except for the Lenser itself)  is the 3 AAA battery - unsuitable and bad.




:shakehead
The P7 is 4 AAA.


----------



## yellow (Jan 15, 2009)

OK, I stand corrected:

_Your primary problem is the *4* AAA battery - unsuitable and bad_



(it makes no real difference, AAAs are far from ideal in most any kind of use, 
except single cell, low output, SMALL lights)


----------



## Fallingwater (Jan 15, 2009)

Since the light is mounted on a handlebar you could run an external connection to a pack of four D cells and solve the "unsuitable cells" problem (you'd still need to swap the resistor to be safe).


----------



## phantom23 (Jan 15, 2009)

Ragiska said:


> but lenser says specifically to not use nimh cells. can you do a runtime on alkaline cells?



Another one - with alkalines and e91 lithium.


----------



## david57strat (Jul 27, 2012)

I'm intrigued by this post, since I own a P7. I haven't had it for very long (maybe two months); but I've started using Sanyo Eneloops, as well, with no problems to speak of. This is not my primary light, so it doesn't see very heavy use; but during the very short periods I use it (maybe a few minutes or so, at a time - if that), it works beautifully, without any heating problems. Because of the warnings of other posters, I've been reluctant to try using the light (with the Eneloops) for extended periods, for fear of messing up the LED. On the other hand, it'd be nice to know just how long I can run the light, on high output, before it actually becomes noticably dim, and/or before overheating may become a noticable issue.

Maybe Led Lenser will someday make an updated design that works flawlessly (and is actually designed for use) with rechargeables. That would be a plus, and it might garner some better feedback from more users on this forum, in spite of its AAA configuration. In the meantime, I'll continue using and EDCing this one (albeit not as a primary light) for those times when I want/need the focusing capability.

I know many CPFers aren't big fans of Maglite or Led Lenser; but these are the only companies I know who actually produce focusable flashlights - and Led Lenser to do a much better job with this, than Maglite do.

Heating issues aside, would it be better to use NiMH (such as the Energizer Recharge), or just continue using the Eneloops? My question applies to run time, mainly. I bought the Eneloops because I liked the idea of low self discharge batteries, particularly in devices (like this P7) that don't get heavy use, but where I want to know it's going to work, whenever I pick it up, without having to worry about the batteries, being discharged (ie, without having to babysite battery voltages constantly. I do that with other 18650 lights lol), as well as for being able to enjoy guilt-free lumens (no more primary batteries having to be tossed out all the time, especially if these go through batteries so quickly, as even Led Lensers on-line specifications would suggest - even with standard aklaline batteries - but preferably rechargeables.

One can hope...


----------



## yellow (Jul 28, 2012)

no "advise" on the main "problem", but who can give You one, when it deals with using cells that are not recommended by the maker?
Also, of course, there should be no direct effects when using the cells, because its not THAT much overpower. Still the damage to the led could happen.

I dont understant the last part with the rechargeables?
When having had the light in some use, or when knowing of a "more/longer than usual" use in the future, one simply puts them into the charger before
:thinking:


----------



## 3Cylinders (Jul 28, 2012)

david57strat said:


> I'm intrigued by this post, since I own a P7. I haven't had it for very long (maybe two months); but I've started using Sanyo Eneloops, as well, with no problems to speak of. This is not my primary light, so it doesn't see very heavy use; but during the very short periods I use it (maybe a few minutes or so, at a time - if that), it works beautifully, without any heating problems. Because of the warnings of other posters, I've been reluctant to try using the light (with the Eneloops) for extended periods, for fear of messing up the LED. On the other hand, it'd be nice to know just how long I can run the light, on high output, before it actually becomes noticably dim, and/or before overheating may become a noticable issue.
> 
> Maybe Led Lenser will someday make an updated design that works flawlessly (and is actually designed for use) with rechargeables. That would be a plus, and it might garner some better feedback from more users on this forum, in spite of its AAA configuration. In the meantime, I'll continue using and EDCing this one (albeit not as a primary light) for those times when I want/need the focusing capability.
> 
> ...



I've run mine on Eneloops from full down to nearly fully discharged with no breaks and have had no issues. It has gotten very warm, but not too hot to hold on to. Eneloops are NiMH, so I doubt you would see any difference with Energizer batteries. It looks like they have updated many of their lights...The X7R is rechargeable, but uses an ICR18650 instead of AAAs now, but puts out 500 lumens.


----------



## david57strat (Jul 28, 2012)

3Cylinders said:


> I've run mine on Eneloops from full down to nearly fully discharged with no breaks and have had no issues. It has gotten very warm, but not too hot to hold on to. Eneloops are NiMH, so I doubt you would see any difference with Energizer batteries. It looks like they have updated many of their lights...The X7R is rechargeable, but uses an ICR18650 instead of AAAs now, but puts out 500 lumens.



Great info, 3Cylinders! Thanks. I like the USB charging capability and the multi-mode capability of the X7R, as well.


----------



## MattSPL (Jul 28, 2012)

I have used my Led lenser P7 as a work light for about 5 years. I have used 4 x Duracell 1.2v NiMH 1000mAh AAA's in it the whole time without issue.

I've never had any problems with heat, and would get at least an hour of full output, then a gradual decline in brightness.


----------



## AnthonyMcEwen2014 (Oct 20, 2013)

Sorry for the necro of an old topic, but I don't like to create new threads when there's an applicable one already made, so I take it the general consensus is you can use NiMH batterys then? 

Only difference is I have the P14 and it takes 4 AA.I only use it for short intervals normally.


----------



## StorminMatt (Oct 20, 2013)

AnthonyMcEwen said:


> Only difference is I have the P14 and it takes 4 AA.I only use it for short intervals normally.



I have a P14 that I've had for a few years now. I admittedly don't use it as much as I did in the past. But I've used it (sometimes for HOURS on end) with rechargeable batteries with absolutely no problems whatsoever.


----------

