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Originally Posted by chrisp9au
2nd question, my battery reads 12V7.5Ah/20HRS, what does the 20 hours signify?
Any and all advice would be appreciated!
Cheers 
Chris |
On your second question, I found this from a pdf, hope it helps.
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Typical ratings for the discharge of nickel-cadmium batteries areover 10 hours and for lead-acid batteries are over 20 hours. Asa result, a rating of 4 or 6.5 ampere-hours for a battery does notmean you can draw 4 or 6.5 amperes from the battery for onehour. The actual amount at the one-hour rate is typicallyone-half the “rated” capacity of the battery, or less. To determinethe actual battery rating, you must take the nominal capacity(4 or 6.5 ampere-hours) and divide it by 10 or 20, depending onthe battery type.In the case of the Model 934 Nickel-Cadmium Battery, you use afigure of 0.4, and for the Model 946 Lead-Acid Battery you willuse 0.325. Customarily, currents below 1.0 ampere are expressedin milliamperes (mA). This means you can expect to dischargethe nickel-cadmium battery at 400 mA for 10 hours. You wouldexpect to discharge the lead-acid battery at 325 mA for 20 hours.Battery manufacturers provide curves in their literatureshowing the discharge rates in percentages of “C,” which standsfor rated capacity in ampere-hours (Ah). If you discharge thebattery at rates greater than the 20-hour rate, you can drawmore current, but for a considerably shorter time; that is, thevalue of time multiplied by current will amount to much lessthan “C.” For more than 20 hours, you can draw less current for alonger time.For times beyond 20 hours, the product of current and time willamount to more than “C,” at least, up to a point. The value of“C,” or more likely a percentage of it, is also used to describe theproper charging current for a battery.
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