Battery energy and discharge rate

battery amp hour calculator:

Enter battery voltage, amp hours, and wattage of appliance

Will calculate run time


Ie 12 volt, 450 AH will run 100 watts for 45 hours

200 watts for 22.5 hours

400 watts for 11.25 hours


Simple uses P= IV and def of amp hour

To what level of discharge does this bring the battery?


Discharge Rate

The storage capacity is expressed in amp hours at a certain discharge rate. The discharge rate of a battery is the amount of time a battery is designed to deliver its full capacity. For example, a 100 amp hour battery with a 20 hour discharge rate is designed to deliver 5 amps. Every hour it will deliver 5 amp hours and in 20 hours it will have delivered 100 amp hours (if it could be completely drained). If the battery is discharged faster, its capacity will be less and if it is discharged slower, its capacity will be greater. If this same 100 amp hour battery was discharged at 20 amps instead of 5 amps its capacity would drop to only 60 amp hours! So, at a 5 hour discharge rate, our 100-amp-hour battery becomes a 60 amp hour battery.


plot of discharge rate vs amp hour capacity;

calculator: for theoretical AH, actual AH for given peukert number and rate of discharge in amps, time in hours to 100, 80 and 20 percent discharge. 20 percent gives longest life


this is the best calculator yet

could use this calculator to make a plot