Are all amp hrs equal?

Gjac wrote:
I assumed this loss in amp hr capacity was due to heat. If this is true, can one also assume that these higher discharge rates producing more heat also reduce battery life every thing else being equal (still only discharging to 50 percent)?

No in fact Peukert's law does not take into account temperature change from self heating. Temperature does effect capacity but that it is somewhat independent of discharge rate. That is if you keep the batteries cooled to a constant temperature during discharge, capacity will still be reduced according to Peukert's law.

"An amp hr at 12v is 12 watt hrs , an amp hr at 13v is 13 watt hrs"

Wait a sec! That is counting the volts twice or something tricky?

A Watt-hour is (volts x amps) x hour while an amp-hour has no voltage. Or something. :)

An amp hr at 12v is 12 watt hrs , an amp hr at 13v is 13 watt hrs
No they are not equal
But more important is the chemical reaction efficiency of the battery

It's related to lead plate thickness and density vs electrolyte
Thick solid plates react more slowly to produce electrical current
A slow low amp draw is very efficient
A higher amp faster draw is less efficient , warmer temps actually speed up reaction and are more efficient until the temp is to high and starts causing battery damage

Porus grid plates expose more surface area aka start batteries, and produce more current faster, but do no recover well from deep discharge, and shed more plate material, and loose capacity

I assumed this loss in amp hr capacity was due to heat. If this is true, can one also assume that these higher discharge rates producing more heat also reduce battery life every thing else being equal (still only discharging to 50 percent)?

BFL13 wrote:
Yes they are all equal. How many you get out of a battery "depends."

Google "Peukert's Law"

Peukert's Law

Interesting, thanks.

Pretty much the same as fuel mileage- floor it and you get less.

Yes they are all equal. How many you get out of a battery "depends."

Google "Peukert's Law"

The lower the rate, the more amp-hours you'll get, except at the very extreme where battery self-discharge comes into play. Trojan, for their T-105, shows these specs:

5-Hr Rate 185
10-Hr Rate 207
20-Hr Rate 225
100-Hr Rate 250

the 230 ah should be based on 20 hr discharge or a constant 11.5A

lower/slower discharge yields more ah
higher/faster discharge yields less ah