Home

Battery Storage Capacity Ratings

Two standard ratings are used to measure a battery’s storage capacity:

AMP HOUR

The amp hour rating tells you how much amperage is available when discharged evenly over a 20 hour period. The amp rating is cumulative, so in order to know how many constant amps the battery will output for 20 hours, you must divide the amp hour rating by 20. Example: If a battery has an amp hour rating of 75, dividing by 20 = 3.75. That battery can carry a 3.75 amp load for 20 hours before dropping to 10.5 volts. (10.5 volts is the fully discharged level, at which point the battery must be recharged.) A battery with an amp hour rating of 55 will carry a 2.75 amp load for 20 hours before dropping to 10.5 volts.


LAMP WATT

AMP HOURS

BASED ON 10 HOUR USE

RECOMMENDED AMP HOUR BATTERY

  6 WATT

0.5 AMP HOURS

5 HOURS

12 HOUR CAPACITY

15 WATT

1.25 AMP HOURS

13 HOURS

33 HOUR CAPACITY

20 WATT

1.75 AMP HOURS

18 HOURS

33 HOUR CAPACITY

25 WATT

2.1 AMP HOURS

21 HOURS

33 HOUR CAPACITY

32 WATT

2.75 AMP HOURS

28 HOURS

55 HOUR CAPACITY

40 WATT

3.4 AMP HOURS

34 HOURS

55 HOUR CAPACITY

RESERVE MINUTES

Reserve minutes is the number of minutes a battery will carry a 25 amp load before dropping to 10.5 volts.  (10.5 volts is the fully discharged level, at which point the battery must be recharged.)

BATTERY AMP HOUR RATING

Most liquid acid batteries are designed for automotive or farm implement applications. These batteries are designed to deliver very large  bursts of current for short periods when starting an engine and then is immediately recharged by the vehicles' alternator. Therefore the battery manufactures do not provide an amp hour rating. Most deep cycle, Gel-Cell and sealed type marines batteries have an amp hour rating that will appear on the battery.


< Previous | Next >