Solar Lights as Battery Chargers

This is kind of a rookie question...  In testing out some solar lights for use in Africa, we found that they come with reusable batteries inside, charge during the day and provide light at night.  However, they can also be used to charge rechargeable batteries that, instead of providing light, can be taken out and used in other devices.  Has anybody been doing this, and do you have any observations or tips?  Do the lights or batteries have to be replaced all the time? I wouldn't say the batteries that come with them are ideal, but higher quality batteries could probably be used.

Hi Mahabba;
I can't say I have heard of anyone else doing that with the yard lights.  But if it is working then do not stop!
I wonder how much charge is going into those battery's and also what kind of battery they are? Lead acid or lithium ion.
Full size solar panels are not very expensive anymore but I could see them being stolen as valuable.  The tiny yard lights are nearly invisible and are very low cost.

I give you an apple for thinking outside the box! Good job!

Thanks Thomas.  We are in an apartment for now, so we have solar lights that we took off the stick.  One is sitting in our window to collect energy for now.  The anti-theft ides had not occurred to me!

It should work just fine. There is a small buck boost circuit in most of them to charge in even so so light. I have changed out some of the batteries that come with them with what I considered worn out nmhd rechargeable batteries and got much better winter use out of them. When I put it on the meter though I noticed mine only charged when the switch was in the on position. That's obvious but in the on position the light then goes on at dusk draining what you made. So if I wanted to use it as a battery charger I would make sure to turn the switch to off at night, and back to on during the day. It would build up slowly but should work.

I have tried this, with decidedly mixed results.

The NiMH batteries in solar lights are very low capacity, typically 600 mAh in an 'AA' size. If you put in higher capacity batteries, they will never charge properly. (For example, the NiMH AA batteries I use have ranges between 2000 and 2650 mAh, almost 4x the capacity. Even AAA batteries run 800-1000 mAh. Sometimes you can get low capacity AAs at dollar stores.)

If you put the solar light AAs in other items, you may find they are slightly smaller or thinner, leading to intermittent contact. Spacers of aluminum foil or paper will help.

Bottom line, for me, is that solar lights definitely cannot take the place of a decent quality charger.

Douglas Alpenstock wrote:I have tried this, with decidedly mixed results.

The NiMH batteries in solar lights are very low capacity, typically 600 mAh in an 'AA' size. If you put in higher capacity batteries, they will never charge properly. (For example, the NiMH AA batteries I use have ranges between 2000 and 2650 mAh, almost 4x the capacity. Even AAA batteries run 800-1000 mAh. Sometimes you can get low capacity AAs at dollar stores.)

If you put the solar light AAs in other items, you may find they are slightly smaller or thinner, leading to intermittent contact. Spacers of aluminum foil or paper will help.

Bottom line, for me, is that solar lights definitely cannot take the place of a decent quality charger.

Do amp ratings matter in this case other then duration of charging? Voltage is the same  for all 5hose rechargeable so that should be what the charger is using. I have not tested this. I do agree it would be of lower quality then a dedicated charger.
Cheers,  David

I've played around with doing that. It was a few years back so probably before NiMH became available. It worked but an actual charger worked better & will probably give better battery life. I would suggest using the type of battery that was originally installed in the light.

David Baillie wrote:Do amp ratings matter in this case other then duration of charging? Voltage is the same  for all 5hose rechargeable so that should be what the charger is using.

Unfortunately, it does. Different battery chemistries (NiMH and LiON) have a specific "charging profile" -- the energy input required at different stages of the charging process in order to charge them fully. A slow trickle charge doesn't cut it, and typically reduces their operating life.

That's why old school lead acid is so friendly for off-grid tinkering. It does not mind being trickle charged by a tiny panel as long as the voltage is high enough. Better to charge an older car battery as the primary energy source, and then run a dedicated NiMH or LiON charger off of that.

Thanks, everyone, for the helpful input!