I just bought a new hair clipper and I was about to start shaving my head when I noticed that it was almost at 0%. It has a nickel metal hydride battery. The manual says I have to load it for 24h hours before using it the first time or whenever it has been unused for a long time.

I started calculating. 24 hours are 1440 minutes. Dividing it by 100 makes it 14.4 minutes to gain 1%. To gain 20% it'll take 288 minutes (more than 4 hours).

Well I started to load it like an hour ago and it has almost 40% so far. That's not 4 hours. So it'll be at 100% in a few hours. I think in the evening it's done.

But the manual emphasized that it should be 24 hours ! So I wondered why do they want me to load it that long even when the percent-bar shows me it's fully loaded and ready to use? I also looked up some reviews where the customers wrote that the battery's lifetime is very short.

Would it cause a shorter battery-lifetime if I use it for like 10 up to 20 minutes in the evening (in about 6 hours)? Or more in general, is there something about the intrinsic chemistry of the battery which requires (in the most cases) so long before we use it the first time? Is that even necessary?

• One thing is, that the battery power is usually measured using it's voltage. However, the voltage/charge is not linear. My notebook Li-on battery spends half of it's cycle at 5%. This all also means, that 100% doesn't need to mean 100%/ Jun 24, 2014 at 21:37

$\ce{Ni(OH)2 + OH- = NiO(OH) + H2O + e-}$