Re: Fenix TK40 part2
Thx HKJ, that's the sort of disadvantage I was supposed to talk about.
So, I guess that would cause some sort of troubles for using nimh batteries? Really unwise to keep 8 nimhs exclusively for the tk40, or another spare set of 8. :thinking:
Actually, this is more likely to cause problems with non-rechargeable batteries because they aren't supposed to be subjected to reverse currents. With NiMHs, all that should happen is the stronger set (of four batteries in series) will charge the weaker set until the voltages are equal. So the voltage and capacity of the batteries in the stronger set will decrease somewhat, and the voltage and capacity of the batteries in the weaker set will or may increase somewhat. Modern NiMH cells also tolerate overcharging at a low rate well, so I wouldn't be concerned about that. Actually, this voltage balancing may be a good thing because it reduces the risk that an individual cell is deep discharged, which is the most common cause of permanent damage in NiMH batteries.
I am assuming, however, that all batteries are of the same brand, type and nominal capacity, and are all about fully charged when first inserted. In particular, if some batteries in one set are nearly empty while others are full, this may cause a significant amount of overcharging. Also, a noteworthy amount of energy will be lost in the batteries from the other set. Moreover, using damaged (e.g. internally shortcircuited) batteries or batteries with polarity reversed could damage good batteries or even the flashlight, so don't do that. Of course, the latter is true regardless of battery chemistry.