The Amp Hour (Ah) rating on a battery indicates the amount of current (in Amps) a battery can provide for one hour. Deep cycle batteries used in RVs typically have an Amp Hour rating of 100Ah or higher. And yes…this implies that a 100Ah battery can provide 100 Amps of current for one hour before it is dead.
But no, you’re probably not going to use all of that capacity in a single hour. So here’s how to apply the Amp Hour rating to estimate how much battery capacity you’ll actually use.
How to use Amp Hours to figure out how long a battery can power your RV?
Each piece of equipment in your RV consumes energy at a different rate. So you’ll first need to calculate (or measure) the total electrical load (in Amps). Then divide the usable battery capacity by the electrical load to get the number of hours.
Length of Time (Hours) = Usable Battery Capacity (Ah) / Total Electrical Load (Ah)
Example: Let’s assume that your RV has a 100Ah battery and a small power inverter to provide AC power. Now imagine that you’re parked at a rest stop watching TV and using your laptop with some lights on.
Question: How long before your batteries dies?
Step 1 – Calculate the electrical load
- Laptop Computer Plugged In (5 Amps)
- LED TV – AC Powered (4 Amps)
- A few LED lights (1 Amp)
- Other miscellaneous things running (4 Amps)
Total electrical load = 14 Amps per hour
Step 2 – Estimate the number of hours you can run this load
When we apply the formula to our example, we see that 7 hours of watching TV and using your laptop will consume roughly 98Ah of your 100Ah battery capacity.
100Ah Usable Battery Capacity / 14Ah Electrical Load = 7.14 Hours
Give it a try. If you add a second 100Ah battery to up your battery bank to 200Ah, how long will the battery bank last?
NOTE: For the sake of this basic example we assume that 100% of the rated battery capacity is available. In reality, we use the term usable capacity to indicate the actual battery capacity available. This varies from one battery chemistry to another. For lead acid batteries (including AGM), the usable capacity is only 50% of the total rated capacity. The usable capacity of lithium batteries is between 80-100%.
What To Read Next
Now that you know what Amp Hours are, let’s figure out How Much Battery Capacity You Need.