# NiMH charging characteristics

#### k1ng 1337

Joined Sep 11, 2020
85
Good Day,

After countless hours of researching NiMH rechargeable batteries I'm still left with basic questions about their charging characteristics, specifically the voltage, current and resistance profiles as they change in response to 1) constant voltage source and 2) constant current source

Can someone confirm these generalizations?

a) assuming no current limiting: the resistance of a charging battery increases as it approaches the charging voltage because there is a diminishing voltage difference across the circuit and therefore a reduction in current

b) assuming a constant current source: as the battery charges, the charger must increase its voltage in order to maintain a constant current because there is only so much "room" and eventually chemical space becomes limited and for the reaction to continue at a steady rate more "input force" is required

c) a and b are really the same process just controlled differently

Thanks!

#### bertus

Joined Apr 5, 2008
21,361

#### crutschow

Joined Mar 14, 2008
27,170
a) assuming no current limiting: the resistance of a charging battery increases as it approaches the charging voltage because there is a diminishing voltage difference across the circuit and therefore a reduction in current
No, the battery resistance likely goes down as it approaches full charge.
But the smaller difference in voltage will still cause the current to reduce.

You should never charge a NiMH battery with a constant voltage, since the initial charging current will likely be much higher than the battery can tolerate without damage.

#### Audioguru again

Joined Oct 21, 2019
3,171
Energizer Battery Company has Technical Info at the bottom of their home internet page. click in a Ni-MH battery of any size and find their Handbook for the battery or for the charger.