Originally Posted By: JHZR2
Originally Posted By: mechtech2
There is a natural increase in voltage due to the cold. There is less resistance in materials [except for carbon].
And sometimes there is an additional design feature for more voltage cold/less voltage hot.
That is backwards.
There is a natural decrease in the voltage. And, since it is a chemical reaction, the reaction slows down and impedance grows in the battery.
But the thing is that onset of gassing goes up higher, from 2.47VPC to 2.97VPC, IIRC, so you have a higher voltage threshold before electrolyzing the water. This is needed to overcome the impedance.
The decrease in voltage in a cold battery is when it is open circuit. When on charge, as in the case of the op, the voltage of a cold battery will be higher.
Conversely, a hot battery will have higher open circuit voltages and have lower on charge voltages, this can lead to a thermal runaway which will quickly damage/destroy a battery.
There is typically an inverse relationship between current and voltage in the recharging of lead acid batteries. The impedance or resistance that you refer to is the direct cause of this.