Which rechargeable batteries?

[kosymodo]

I have some solar garden lights. Some of these aren't currently working, so I pulled the batteries and tried charging them in my wall charger. They all got flagged as being faulty :/ So, since batteries are cheap enough, I'm going replace them.

The original batteries are 150mAh. Searching for new batteries, I can find lots of 2300mAh/2400mAh, then some 600mAh at a higher price. Can I use the 2300mAh batteries? I assume that the only thing to note would be that the batteries wouldn't ever charge to 100% due to the limited charging capabilities of the solar cells?

 

[kosymodo]

The reason they use such low capacity batteries is that they are better suited to being recharged by small solar panels, higher capacity batteries take more current to charge.

To charge to full, or to charge at all?

 

[kosymodo]

What are the batteries in the lights?

Many solar garden lights use low density (mah) NiMH batteries which require lower voltage to recharge from the solar panel, if you changed to Li-ION with significantly higher energy density (2000+ mah) they require a higher voltage to recharge than the solar panel is likely to provide so will just end up dead and once they drop below a certain voltage the internal resistance increase substantially which could result in excess heat and eventually a fire/exploding cell.

A large energy density battery will indeed last longer, but if the battery is unable to charge due to insufficient voltage, it will just end up a dead battery.

As far as I know NiMH cells charge at ~1.2v and Li-ION cells charge at around 3.6v+

Check the battery type and go for a slightly higher capacity in the same type.

I'm guessing these are very low end nicad batteries in the lights, in which case going with nimh would be overkill and may not work properly. Usually batteries will state the type somewhere on the label, as not all batteries can be charged safely using the same chargers.


It'll almost certainly be because the cost but also knowing people aren't going to complain the light doesn't stay lit for more than half an hour.
I'm guessing they're being made using what are effectively junk batteries that have either failed QC, or from a production line that can't make anything else so they're making batteries that are 30 years behind the times in terms of technology (I've seen batteries in these things that had lower capacity than a mid range battery when I first started paying attention to rechargeable in the late 80's).

A higher capacity in bulk probably wouldn't cost much more, even just a cent, but that's a way to save.

Personally if I had them and I wanted to improve them i'd probably look for something with a higher capacity in the same battery tech if just because if they're using nicad the memory effect is going to be nasty with the sort of charge cycles they'll get over the winter.

The current batteries are Ni-MH

I'm gonna try spending a bit more then on similar capacity batteries, again Ni-MH, and let's see what the results are!