As you can imagine, having a very accurate picture of your daily amp usage is critical to inform your buying decision. For this, you need to take every piece of appliance in your RV and determine two things: how much amp it consumes per hour
and how long you plan to use it for, on average.
First, make a list of every appliance you have onboard (an Excel sheet comes in handy). The amp usage and other information are usually stamped somewhere in the product or box, or you can consult your user manual if you have it. Worst case, you'll find what you need online.
Can’t see an amp rating? You can take the stated watt and voltage rating and get the amp per hour rating using the formula:
watts / voltage = amps
So an appliance with 100 watts and 12 volts roughly consumes 8.3 amps per hour (100 watts / 12 volts = 8.3 amps)
After you’ve determined your amp usage for all your appliances, you need to think about how often you use each of them in a day. You can calculate it using this handy formula:
amps per hour X hours used per day
For example, let’s say the 4 lights you have in your RV need 0.3 amps/hour each to run and you use them for 8 hours. Your daily AH consumption would then be 9.6 amps per day (4 lights X 0.3 amp per light X 8 hours = 9.6 amps per day)
In the same way, a 10 amp per hour device used for only 15 minutes will lead to a daily drain of 2.5 amps per day (15 minutes being ¼ of an hour X 10 amps = 2.5 amps per day)
Finally, it’s a matter of adding up the amp per day consumption of all your appliances to get your daily AH usage. Simply add 20% to this number, and you have the minimum AH for the RV deep cycle battery you need to get.
(Whew! That was one long but necessary explanation – good job for sticking through!)