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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 their life span?
Based on this article, it sounds like the NiMH batteries could be safely used with a charging system that is designed to slowly charge NiCad batteries.
However, the lifetime of a NiMH battery charged that way may be poor compared with a NiCd one. The same question was asked in a battery forum, and one of the responses was:
The cheaper priced NiCd is a good option.
I think the problem with eneloops in solar garden lights is not overcharging but over-discharging. The capacity is too high for them ever to reach a full charge in a day of sunlight, but at night the lights will run them right down to empty and beyond. NiCd can take deep discharge cycles much better than NiMH can.
However, obviously not everybody is in agreement with this. This other site seems to say it's a great idea to replace NiCd's with NiMH batteries instead. Maybe it depends on the brand?
I don't know who's correct about which is better, however I do know that NiMH batteries quickly deteriorate if left fully discharged. If you're going to put a solar light (containing an NiMH battery) into storage, allow it to charge up at least partially first.
If you ensure NiCd batteries are correctly disposed of, the potential environmental impact is heavily reduced.
NiCd batteries are only bad for the environment if you discard them. NiCds suffer from a memory effect, so it may be possible to rejuvenate them with an appropriate charger - one that has a "refresh mode". (I've done this myself, and am still using some batteries that I know are more than a decade old.) Several such can be found with Google.
The problem with using NiMH batteries in place of a Ni-Cd in a solar light. NiMh charge at a higher voltage which means they will not receive a full charge if much at all and will not last very long when the sun goes down. Is best to use the same type of battery that the solar light was designed for.
