What are Protected and Unprotected Li-Ion cells?
Both Ni-Mh and Li-Ion cells will be permanently damaged if the voltage is allowed to drain too low, or is charged up too high. Damaged batteries can heat up and catch fire when charged; LiIon being the more severe of these two. Protected batteries include a very tiny electrical circuit on the end of the battery that limits the highest and lowest voltage the cell can reach during use; thereby adding a safety feature. In many cases it will also limit the peak current allowed if the battery ever shorts out. So to say cell protection is a good thing would be an understatement! Li-Ion battery packs should always incorporate some form of circuit protection.