Add up the watt-hours your RV uses in a day, divide by 12 for amp-hours, then double it so the battery is drawn down only halfway, as Renogy recommends. A 35 W fan for 6 hours comes to a 35 Ah battery.
Renogy’s steps
- Multiply each appliance’s watts by its hours: Renogy’s 35 W fan for 6 hours uses 210 Wh.
- Divide by 12 V for amp-hours: 210 ÷ 12 = 17.5 Ah.
- Double it. Renogy recommends a depth of discharge of only 50% to help the battery last, so 17.5 Ah becomes 35 Ah.
Battle Born lists the things to add up: the fridge, lights, CPAP, coffee maker, TV, laptops and anything on the inverter. The power station size calculator gives the 12 V amp-hours for any watts and hours, the step before Renogy’s doubling.
Lithium or lead acid
Battle Born says one of its 100 Ah lithium batteries gives nearly the same usable energy as two similarly rated lead acid batteries, because lithium can routinely use nearly its full capacity without shortening its life.
To check how charged a 12 V battery is, measure it at rest and compare it with the battery voltage chart.
Fitting the space
Battle Born recommends taking stock of the battery space in your RV first. Its batteries come in sizes that drop in for lead acid group sizes.
| Battle Born battery | In place of |
|---|---|
| 75 Ah, 12 V | Group 24 lead acid |
| 100 Ah, 12 V | Group 27 or Group 31 lead acid |
| 270 Ah, 12 V, GC3 | 8D lead acid |
Battle Born strongly recommends against mixing batteries of different amp-hour sizes.