Glossary

House battery

Also Service battery, Leisure battery

What is House battery?

The battery that supplies the loads on board. It is designed for many cycles at moderate current — unlike the starter battery, which briefly delivers very high currents.

What matters about House battery in practice?

House and starter batteries are kept separate and charged together via a split-charge relay, an isolating diode or a DC-DC charger. This way the load side can run flat without the engine failing to start.

Its size follows from the daily balance and the permitted depth of discharge, not from the space available.

Which battery types suit a service battery?

Deep-cycle batteries: AGM, gel or LiFePO4. Classic starter batteries are not built for this and quickly lose capacity with regular deep discharge. LiFePO4 offers the greatest usable capacity at the lowest weight.

How large should the service battery be?

Daily consumption times days without recharging, divided by the permitted depth of discharge. At 80 Ah a day and two days of autonomy that is about 320 Ah with lead, about 200 Ah with LiFePO4.

How is it charged?

  • On shore power via a charger with a suitable charging profile.
  • While driving via a split charge relay or, for lithium, via a DC-DC charger.
  • From solar via a charge controller.

The page LiFePO4 battery for boats describes how to switch to lithium.

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