# Help: Need battery upgrade for outdoor solar light



## chaosdsm (Nov 2, 2019)

Finaly ready to upgrade the batteries in my solar powered outdoor light (5.2V 10.5W panel output on a good clear day). It currently has two "SLM-CT 3.7V 2400mAh" 18650 batteries installed in Parallel from the factory. There's room in the battery bay to install 3 batteries. So which is my better option??? 






Pink battery pulled from a laptop - just there to make sure there's clearance for a 3rd battery & still room for the wires.


1> Install 3 new 2400mAh - 2800mAh batteries in Parallel for increased runtime. (I'm sure the panel wouldn't charge 3 3000+ cells very well)


OR 


2> Install 2 new high capacity 3400mAh - 3600mAh batteries in parallel for increased runtime. (I'm thinking this option probably better overall)




AND: Which 3.7V chemistry would be the best to use in a solar charged light that gets 4-6 hours of direct sunlight (assuming no clouds) each day??




On a good cloudless day of charging (8 months after the cells were fully tested and charged), the light will run for about 9 - 10 hours overnight, but we're getting about 13 hours of night. It's being used as a flag light, for a US flag that is up from May 8th through through Dec 7th.


Ideally, I would love to upgrade to a light that could run year round (excluding hurricane landfall), but none in my price range give enough light continuously.


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## Lynx_Arc (Nov 2, 2019)

You are probably better off having more battery capacity than your panel can produce a day that way the batteries are not completely charged which should increase the total number of cycles it will charge. If you want more runtime you probably need about 50% more battery capacity and 50% more solar output. One other option would be to hook up an external charging circuit on a timer that kicks on for a few hours when the solar panel is not putting out much power. This would cost you a little in electricity but could be a lot cheaper than investing in another panel and you could adjust the timer to give you more runtime till you get the runtime you need.


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## chaosdsm (Nov 7, 2019)

Okay, so the plan is: 
> purchase tomorrow: one - Keystone 1048 (PACK OF 2) Dual 18650 battery holders with gold plated contacts from Amazon. 
> cut existing wiring to batteries since the current batteries are hardwired
> solder the existing wiring leads to the new holder
> use a pair of Orbtronic 2900mAh Protected "High Drain" 18650's I already have (but rarely use) for my bike light, to see if it will work as expected.

*And if anyone knows if a specific 18650 chemistry (other than LiFePO4) is better suited to daily full usage and solar charging, I'd love to hear it.*


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## chaosdsm (Nov 15, 2019)

All finished and works great! 3 days in a row, light has still been on at dawn, though it did appear to my eyes to be somewhat dimmer on the 3rd day. As the nights get longer and longer, I don't think the 2900mAh cells will be enough to run a full night every night through December 7th. Fortunately with this setup, it'll super simple to swap batteries!

Here are the Keystone 1048 holders I purchased. They are not designed for protected cells, but they do just barely fit, and now I have an extra holder for potential future project! 





Here's the old cells I pulled out.





After I removed the wires, I threw them on the Opus charger, and turns out one battery was bad.


And here is the battery carrier installed. I had to make a slight modification to the inside of the battery compartment to get it to fit inside, but it works!


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## Dave_H (Mar 13, 2020)

Interesting mod, BTW what current drain does the lamp have? Looks like the battery bank charges at about 2A peak.

When you say "other than LiFePO4" not sure what else is commonly available in 18650. 

I have a rope light with 90 small LEDs using small 9 sq. in. amorphous panel charging a single 14500 LiFePO4. The lights are set to a bright/dim pattern so not on full brightness all the time, and in summer they usually stay on until ~2am, so about 5-6 hours operation; not too much less in winter. It's been running for over a year, so far so good.

LiFePO4 has lower voltage, but is fairly common for garden lighting (except the cheapest). You'd have to check available capacity (and price/availability), and if your setup can work with the lower voltage (need to mod the charger if feasible). Moreover, capacity seems to be low, probably only half what you have now, may not work for your case.

Dave


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