Originally Posted by Roy in TO
OK, maybe I'm dumb. I read the specs for his fridge
and got the avg amps per hour.
If I've got a battery
rated at 100 amp hours and I don't want it to go below 50%, my understanding is that I can use 50 amp hours. Given that his fridge
consumes about 1 amp per hour. Should I not be able to run his fridge
by itself for about 2 days before I need to recharge the battery
Roy, you are not dumb, you get an A- though, instead of an A. As Thomas explained, you need to take the Peukert exponent of the battery
into account to get the exact duration under a particular load but your method gives a really good guess under "moderate" loads.
The amp-hour capacity rating is usually the 20 hour rate. That means your 100 ah battery can put out 5 amps for 20 hours until it is functionally dead (usually 1.75 volts per cell or 10.5 volts for a 12 v battery). Note this means that if the actual load is less than 5 amps you get a little more than the rated amp-hours.
The comment about 'watts' being being the correct unit is true but not relevant here as pretty much everyone here uses a 12v battery system.