Wiring Batteries in Parallel for a Van or RV: How and When
Once a single battery doesn't cover your house battery needs, the next step is usually two (or more) batteries wired in parallel — same voltage, combined capacity. Here's how to do it correctly.
Size your battery bank
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Parallel = same voltage, more capacity
Wiring batteries in parallel (positive to positive, negative to negative) keeps the voltage the same (e.g., 12.8V) while adding the amp-hour capacities together. Two 100Ah LiFePO4 batteries in parallel give you 200Ah at 12.8V.
This is different from series wiring, which adds voltages together (used to step up to 24V or 48V systems) — most van builds stay at 12V and use parallel for capacity.
Match batteries exactly
For a parallel bank:
- Same brand and model — internal resistance and BMS behavior should match closely.
- Same age — mixing a new battery with a used one means the used one ages faster, dragging down the whole bank's performance.
- Ideally purchased together — some manufacturers specify a maximum number of units that can be paralleled and how to wire them for balanced current sharing.
Don't mix battery brands or chemistries in parallel
Different brands/models of LiFePO4 can have different charge/discharge characteristics and BMS cutoffs. In a parallel bank, the weakest or most different battery can be over- or under-stressed relative to the others, shortening its life and potentially causing BMS faults.
Wire each battery to the bus bars individually
Rather than chaining battery-to-battery-to-bus-bar, run each battery's positive and negative directly to the bus bars with equal-length cables of the same gauge. Equal lengths help ensure each battery shares the load evenly — a shorter cable to one battery means slightly lower resistance, which can cause it to take more of the current.
Fuse each battery individually
Each battery gets its own fuse on its positive cable to the bus bar, sized to that battery's max continuous discharge/charge current (per its datasheet) — not a single fuse covering the whole bank. This way, a fault on one battery's cable doesn't take out the entire system, and you can isolate a single unit for troubleshooting. See fuse sizing.
When to go parallel vs. one bigger battery
| Choose | When |
|---|---|
| Single larger battery | A single unit (e.g., 300-400Ah) covers your needs — simpler wiring, one BMS, one set of terminals |
| Parallel bank | You need more than the largest available single unit, want redundancy, or are expanding incrementally over time |
For most US builds, LiTime and Battle Born both offer larger single units (200Ah+) that cover the needs of two smaller batteries in parallel — check if a single larger unit meets your sizing before defaulting to parallel.