Quote:
Originally Posted by Al Skierkiewicz
Amp Hour is a rating that specifies how long the battery will deliver current until the terminal voltage reaches a certain level (@25 degrees C and that level varies from manufacturer to manufacturer.) It does not specify the max current nor does it indicate a time at any current other than that shown. It is typically measured at 1/20 of the amp hr rating. That is an 18 amp hour battery delivering 1/20*18 amps= 0.9, amps will take 18 hours to reach ~8 volts. At higher currents, the time decreases.
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Not exactly, Al. While the principle is the same, the Ah rating comes from the maximum constant discharge possible over a specified time period (20 or 10 hours, usually) falling to a specified terminal voltage. So an 18 Ah battery can deliver 0.9A for 20 hours, ending at about 8 volts. (But, in agreement with Al's point, that does NOT mean 1.8 A for 10 hours...)
20 hours is usually used for larger batteries, 10 hours for smaller ones. You need to read the specs o see what the manufacturer used.
Also the exact ending voltage is a standard, but I don't have that info handy at the moment. It is around 8 volts though.