Hi all, Nimh and Nicad are rated at the 5 hour rate. The example quoted gives you a good idea of what to expect. 4000mAh. take the 4000 and divide by 5 (hours) = 800 (m.amps) so the battery will give you 5 hours at 0.8 amps (800 mamps)
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If you want more current then the battery is less efficient and will run for less time than say 4 amps for 1 hour. The extra power going into warming the battery, a good clue as to taking too much current at once. The whole process of re-charging needs 40% extra current to give a full charge.
Lead acid cells are rated at the 20 hour rate so do not appear to have the same power.
Spiral wound cylindrical lead acid cells are rated at the 5 hour rate.
A word of warning if you are buying from China, you cannot rely on the battery label as to capacity. If suspicious after purchase weigh them in compaison with a known quality battery, they are much lighter, i.e less content.
After getting caught a year or so back with labels saying 3800mAh which when measured turned out to be 1450mAh, I rely on our well known British suppliers. You pay more because you get more.
regards Roy