Can I use ni-mh batteries in my garden solar lights?

The solar light batteries in my garden are dead. Upon replacing them, I realized they were the old Ni-Cd rechargeable batteries.
I have heard that these batteries are not so good for the environment because they contain toxic chemicals (see Wikipedia). I would like to use Ni-MH batteries instead.
Would this be recommended or will slowly charging these batteries using solar panels shorten its life span?

Yes, they will work fine

I just bought Eneloop lites for that purpose.

The Lites are supposed to be tougher and will charge 5,000 times.

NIMh will work fine. Even alkaline will function for a good while. The stock batteries are usually poor quality. It’s an abusive environment. Personally I use my over the hill NiMh and expect a limited life span.

Does the charging function work the same way for both NiCd and NiMH?

I have solar powered cat scarers, and I suspect the case will leak, damaging the batteries, at which point I will probably buy more scarers, keeping the solar cells in case I find a use for them.

Attempting to charge alkalines will increase the chance of them leaking.

You can use NiMh, standard Alki’s should not be re-charged. NiMh does normally require a different charging profile than NiCad but with the low charging current involved here nothing bad will happen to swap them around. Cells with the lowest charging resistance will do best for the same reason. High capacity cells probably won’t fully charge so I’d go for something no more than 1.5-2X the ma rating of what it came with. In mine I just dump in whatever I have handy and swap for fresh if performance drops. All my NiMh AA’s are cheapies and rather old anyhow.


True. But someone in this group indicated it actually worked, so I’m trying it on a limited basis. So far, works as well as crappy original NiCads (better probably) and no leaks. BUT….the leak risk is higher, so I don’t advocate it by any means. The cost level I have in my solar chargers is not worth wasting the likes of Eneloops on them.

At the v…e….r….y s….l……o……w rate you are charging batteries with these devices it’s irrelevant whether there is NiMh or NiCad in there. The rate is so slow you probably can’t charge a high capacity NiMh in a single day. Once the days shorten I have to pull them and put them in a charger weekly if I want them to work. I determine that by when they go dead usually :stuck_out_tongue: . So far they’ve always revived and continued to work. Amazing actually.

Your used alkalines are good for blackouts, when you bring a couple of your garden lights into the house, or dig out a few of your old/ugly garden lights that you stored away instead of trashing, the solar garden lights run for days. on alkalines.

I have replaced so far all batteries in my solar lamps with nimh.
I used ikea laddas and some different brands all stock batteries were crap.
I had some which were so lightweight that they reminded me on the AA spacers which only have a hollow metal tube. It makes sense to clean the contacts and use some contactspray which prevents corrosion like wd40 or similiar.

I also replaced some leds with great sucess, the stock lights usually use very blueish leds and they corrode after a decade.
If the solarcell has lost the shiny glare you can spray paint them with clear coat after that they will look like new. Of course all this make just sense if the whole light is a nice one, the cheap 1.99$ plastic ones are the best if you let them in the store…

I have some very old lights which are made out of stainless steel and have a very nice electronic with 2AA in series which work reliable and bright.

You used to be able to buy a charger for alkalines, a decades or two ago, in Britain anyway. I noticed one is still for sale, not sure if it is the same brand:

But I do wonder what is the point, since they are liable to leak, especially when multiple cells are in series, and rechargeables don’t cost much more, and last ages. We use Duracells in our mice at work, and they usually leak, sometimes when in the mouse, but most often in the paper recycling bag.

I have one. Indeed, it does increase the likelihood of leaking substantially. The more often the battery is ‘cycled’, and the more discharged before cycling (it does reject batteries that are too low), the higher the probability of leaking. I would not recommend them to anyone. Leaking alkaline are a big enough problem without making it worse.

I use mine exclusively as a ‘sorta-smart’ low amp charger for some batteries. It’s pretty much one of those put it in and forget it type since it charges so slowly the possibility of problems is about nil, and it does shut down charging.

Mine is completely different looking than the link provided.

Have any of you seen the awesome build using supercapacitors that will completely charge in about 4-6 hours, and run for at least 12, and NEVER need batteries, and if encapsulated will last over 20+ years?

in fact this guys entire video series is really awesome!

Cool idea with the super-caps !
All my solar lights are cheapies, usually last 1-2 years. But I’ve got one 2XAA which had been going for around 10 years and another single that’s been going about 6. Getting nigh-on impossible to find 2-cell cheapies but those were always better in both run-time and lifetime.

My last running 2xAA is named “Whitefish Light” because it’s on a striped post and I use it to safely guide my “work freighter” as I’m backing into it’s parking spot. It’s a tight fit, fenced on 3 sides with only one front door that can be opened once it’s in there for security reasons. No, my truck ain’t named Edmund but it probably gets the same fuel mileage!


I wanted to reply this to your original thread but it got lost in translation…
From my calculations super capacitors have very small capacity which most people seem to ignore because on the first look we all think they are awesome and have grown up fast…

He used 500Farad caps which have an energy like this:
500F*2.5V=1250Ws. 1250Ws/60/60=0.35Wh

Even if he charges them above 2.5V and uses 2 it is way below 1Wh. Just for info one eneloop has 2.4Wh and one 18650 has 10Wh.
If I had time to play with such things I would use a 18650 cycled very flat and I am sure this will be smaller and last also forever and would have additional capacity of used indoor for some days without charge…

So what mistake did I make?

I read somewhere that nicads work better than nimhs at low temperatures, or something like that.

not sure, just thought it was really cool, his initial tests ran for 1.5 hrs on 20F

Seems my calculations were not correct but the Overall result is the same very low energydensity. The cycle count seems to be extraordinary hi and it seems that these are not destroyed if underdischarged.
Here is an online calculator:

The one in the resin block he build is kind of cool…imagine some future archaeologists digging that out…

I think the advantage here would be never having cell degradation and loss through use. Caps should last forever. It would take a lot for equal output to a pair of AA’s, but we’re not talking a lot of lumens.

I see a future project coming for me!

Charge /discharge.cycles measured in hundreds of thousands, mppt charge controller ensuring it doesn’t overcharge and damage the capacitors…how many years is 100k + days? Encapsulated so no oxygen/moisture degrade the components…short of EMP or a magma flow….infinity light is pretty aprapos…