# Lead Acid Battery "Internal Resistance" and Temperature

by thender
Tags: acid, battery, charging strategy, h2so4, internal resistance, lead, lead acid battery, temperature
P: 22,708
It is a matter of changes in ionic conductivity. See for example

http://en.wikipedia.org/wiki/Electri...ure_dependence

(not an explanation per se, but it shows how large the changes are as a function of temperature). Lead plates can be safely ignored.

During cranking it is an ohmic drop, AKA ohmic loss, AKA IR drop. To quote wikipedia:

 The magnitude of the emf for the battery (or other source) is the value of this 'open circuit' voltage. When the battery is charging or discharging, the emf itself cannot be measured directly using the external voltage because some voltage is lost inside the source. It can, however, be inferred from a measurement of the current I and voltage difference V, provided that the internal resistance r already has been measured: ℰ = V + Ir.
emf stands for electromotive force (http://en.wikipedia.org/wiki/Electromotive_force).
 Engineering Sci Advisor HW Helper Thanks P: 6,385 In practice, you don't need much "strategy" for charging lead acid batteries. So long as the charging current is fairly low (say less than 5 amps) you can overcharge a typical car battery for ever, without harming it. So all you need to do in practice is to make sure the charging voltage is low enough so the charging current is low when the battery is fully charged. That's what the voltage regulator on the car alternator does. The usual voltage is about 14V. The charge taken from the battery to crank the engine is replaced fairly quickly (e.g. in 10 to 20 minutes) and the rest of the time the battery is being harmlessly overcharged. Note that while the engine is running, the power for the car electrics like the lights, aircon, sound system, etc is coming from the alternator, not from the battery.
P: 13

## Lead Acid Battery "Internal Resistance" and Temperature

Hi Thender...

This may help: - http://batteryuniversity.com/learn/a...d_acid_battery

Cheers

Malc