One 12V 300Ah battery or two 12V 150Ah in parallel for a van build?

Direct answer: Both approaches can deliver similar energy: one 12V 300Ah pack (about 3.84 kWh at 12.8V) or two 12V 150Ah packs in parallel (about 1.92 kWh each). Choose one large battery for simpler wiring and fewer interconnects, or two in parallel when you need redundancy, easier lifting through a small hatch, or a thin form factor such as the 12V 150Ah EU thin size. If you parallel, match SOC before connecting, keep cable lengths equal, and fuse each battery.

Energy and current. Nominal energy is similar either way. What differs is how current shares and how hard each BMS works. A single 300Ah pack carries the full inverter and DC load through one set of terminals and one BMS. Two 150Ah packs share current only if cabling is symmetrical; unequal cables mean one pack works harder and may hit current limits first.

Physical fit. Prior articles note the standard 12V 150Ah around Group 31 footprint and the EU thin size at roughly 552 × 110 × 288 mm for tight skirts or seat bases; confirm the latest drawings. A single 300Ah case may be easier electrically but harder to lift into a high cupboard. For related capacity-choice thinking on other platforms, see choosing among capacity steps.

Redundancy. If one paralleled battery opens on protection, the other may still run essential loads at reduced capability. A single pack is a single point of failure unless you also carry a jump pack or second bank.

Cabling practice. Use equal-length positive and negative cables to a common busbar, correctly sized fuses at each battery positive, and a main disconnect. Do not daisy-chain heavy loads off one battery’s terminals while the other only sense-wires in.

Balancing and maintenance. Parallel LiFePO4 packs should be at similar SOC and voltage before paralleling; after install, periodic checks of individual voltages catch a weak unit early. See matching SOC before paralleling.

Charge limits. Confirm each model’s continuous charge rating and set the charger or DC-DC below the bank limit. Parallel banks add capacity but do not automatically double every model’s allowed charge current unless the supplier says so.

When one 300Ah wins. Simple vans with one inverter, good access for a heavy pack, and no need for modular replacement usually favour one battery.

When two 150Ah win. Narrow compartments, DIY installs where two lighter lifts are safer, or owners who want to replace or expand one module at a time.