The Magicshine has a 2s2p battery pack -- two cells in series, two in parallel.

Cell reversal is an issue for NiCd/NiMH cells -- the weakest cell's voltage drops to zero, but the other cells keep things going, so it gets `reversed' which makes it even weaker. But if you have eight cells, and one goes bad, you still have seven good cells so the voltage reduction is relatively minor.

However, it's unlikely to ever be an issue with a 2s pack, simply because by the time one cell is dead, you're looking at less than half the original voltage, probably significantly less, and usually whatever is powered by the battery is already not working any more. And the protection circuitry makes it even less likely to happen.

LiPos/LiIons don't actually have to be reversed (dropped to zero volts and beyond) to be damaged -- they're damaged by going under 3 volts (or over 4.2 volts.) The protective circuit should prevent both conditions from happening -- and yes, it may kick in and make the cell entirely non-functional -- it may never work again, unless you bypass the circuit and charge the cell somewhat. This is done because abused LiPo cells can, under some conditions, catch fire and nobody wants that.

NiMH and NiCd cells are fine with being discharged to zero (but going beyond is bad) and are also fine with being overcharged as long as the charge rate is low. So they don't really need any protective circuitry. But LiPos certainly do ...

In any event, if one cell's circuit decides that this cell is no longer good, it basically takes it out of the picture. This reduces the capacity of your pack by one half. The way one tests this is by using a volt meter to check the individual cells ...