Replace solar lamp battery with protected cells?

You all know these cheap solar lamps which are dead after one winter. Why are they dead? Because they over charge the batteries every day in the summer und deep discharge them every day in the winter.

Mine have 18650 1200 mAh Li-Ion cells in them. They charge to 4.5 V and are very dimm but still lit at 2.5 V. So I was thinking, what if I replace the dead batteries with protected cells? Would the over charge and over discharge protection save the cells, or would the protection kick in once and the light is dead?

I`m not sure about the overcharge thing (never tested it) but the discharge is fine, it just turns off the battery until you add power again.
Also the temp extremes are also likely to damage them too.

I've never seen a set with Li-Ion cells in them, I suppose some might. NiMH cells would be a better choice for the exposure to the elements. The reason they only last one winter is because they are cheap. There is no real circuitry inside them, just a few components to make everything work.

Any half-way decent solar light that uses lithium-ion cells, should have a circuit that cuts off at low-voltage, and a circuit that prevents over-charging. It's probably a 50 cent chip, and I've seen them in solar lights.

If you're certain the cells are charged to 4.5v, and you're not just reading the PV voltage, then you have a serious safety hazard there. Don't use it.

The light were cheap, but not extremely cheap. I mean, they have an 18650 cell in them and not just a AAA. I measured the 4.5 V across the battery with indirect light on the panel. But to be honest, the battery was already shot at this point. When I covered the solar panel the voltage dropped to 2,5 V and the LEDs glowed dimmly. I will put a metal plate behind the lights so they dont burn down my wooden garage.

worldedit said:

The light were cheap, but not extremely cheap. I mean, they have an 18650 cell in them and not just a AAA. I measured the 4.5 V across the battery with indirect light on the panel. But to be honest, the battery was already shot at this point. When I covered the solar panel the voltage dropped to 2,5 V and the LEDs glowed dimmly. I will put a metal plate behind the lights so they dont burn down my wooden garage.

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Okay, that sounds like you were measuring the voltage that the PV panel was providing, not the voltage of the cell. The unit may have proper over-voltage protection. IMO, I'd just replace the cell with something similar. You could try protected, but it's probably not needed, and in fact the unit may not be able to charge it if the low-voltage is tripped.