For most campers, a Group 27 or Group 31 lead-acid battery—or a 100Ah lithium—is the right starting point, sized by your daily energy use.
Choosing a camper battery by length of your rig or the size of the tray is the most common mistake people make. The right size depends on what you power, how long you camp off-grid, and the battery chemistry that fits your budget. Sizing a camper battery means matching a physical group size to your calculated daily load, not the other way around.
How to Calculate the Battery Size You Need
You can estimate the minimum capacity in five steps, starting with everything you plan to run. The formula works the same for every camper.
- List every 12V load you use—lights, fridge, furnace fan, water pump, phone chargers.
- Estimate each device’s daily watt-hours (watts x hours used per day).
- Divide the total watt-hours by 12 volts to get daily amp-hours.
- Apply the chemistry’s depth-of-discharge limit—lead-acid gives you about 50% usable capacity, while LiFePO4 lithium gives 80–90%.
- Multiply by the number of days between charges, then add a 10–30% safety margin.
Common Camper Battery Group Sizes and Capacities
The table below shows the standard North American BCI group sizes that fit most camper trays, with typical capacities. These are the shapes you’ll see in any dealer or parts store.
| Group Size | Typical Capacity | Physical Size (L x W x H, inches) |
|---|---|---|
| Group 24 | 70–85 Ah | 10.25 x 6.8 x 8.9 |
| Group 27 | 90–110 Ah | 12.1 x 6.6 x 8.9 |
| Group 31 | 100–125 Ah | 13 x 6.8 x 9.4 |
| GC2 (6V) | 180–230 Ah (pair wired in series) | 10.4 x 7.1 x 10.9 |
| 8D | 200–250 Ah | 21 x 11 x 10 |
BatteryStuff.com’s BCI group-size chart confirms that Group 24, 27, and 31 are the common RV battery sizes, with the larger 8D reserved for heavy commercial or high-load setups. Many weekend campers land around 100–200 Ah total, which usually means a single Group 27, a Group 31, or a pair of 6V GC2 golf-cart batteries wired in series for 12V output.
Matching Battery Size to Your Camping Style
Your camping style is the fastest shortcut to a starting size. Fullriver’s guidance breaks down neatly into three typical use bands:
- Mostly hookups: A Group 24 or Group 27 AGM is usually plenty, since the shore power handles the heavy loads.
- Weekend boondocking: A Group 27 or Group 31, or a 100Ah lithium, covers a couple of nights without charging.
- Regular off-grid with furnace and fridge: Step up to a Group 31 or a 100–200Ah lithium bank to run the constant draws.
Lead-Acid vs. Lithium: What Changes Your Choice
lithium is about usable capacity and upfront price. A 100Ah lead-acid battery gives you roughly 50Ah of usable power before you risk damage. A 100Ah LiFePO4 gives you 80–90Ah. That means a smaller, lighter lithium battery can replace a larger lead-acid one for the same real-world runtime.
Switching from lead-acid to lithium also means checking converter and charger compatibility. Many older camper converters charge at a voltage profile designed for lead-acid, and they won’t fully charge or may eventually damage a lithium battery. In that case, a lithium-compatible converter or charger upgrade is part of the cost. Renogy’s battery size chart walks through the same sizing math and warns about inverter losses and charger compatibility as common oversights.
When you’re ready to buy, our tested roundup of the best battery for a camper compares the top models in each group size.
References & Sources
- BatteryStuff.com. “BCI Battery Group Sizes Chart.” Confirms standard RV group sizes and physical dimensions.
- Fullriver Battery. “What Size Battery for My Camper?” Provides the sizing formula and typical use bands.
- Renogy. “Battery Size Chart.” Covers sizing math, inverter losses, and charger compatibility.