Leisure Electrics
What is a Split Charge Relay / B2B Charger?
The clever switch that sends spare engine power to your leisure battery as you drive.
Simplified animation — not to scale.
In plain English
This is what stops your engine battery and leisure battery being connected all the time (which would flatten both). It only lets power flow to the leisure battery once the engine is running and the alternator is producing enough to spare.
How it works
Older vans use a simple relay triggered by the ignition. Newer vans — especially those with 'smart' alternators — use a DC-DC (B2B) charger, which manages the voltage properly so the leisure battery actually reaches a full charge instead of stalling at 80%.
Signs of trouble
- ⚠Leisure battery barely charges even after a long drive
- ⚠Warning light for 'split charge' or 'auxiliary charge' on the panel
- ⚠Leisure battery voltage doesn't rise when the engine starts
Rough UK cost
£150 – £450 fitted, more for a lithium-compatible B2B charger.
Ballpark only — depends on your van, converter and local labour rates.
Heads up: CamperAutonomy is for general guidance only. Anything gas-related must be signed off by a Gas Safe engineer with LPG endorsement.
More in Leisure Electrics
Leisure Battery
The separate battery that runs your lights, water pump and fridge — without you ever waking up to a dead engine.
Battery Monitor
The little screen (or app) that tells you how much power you actually have left.
12V Fuse Board / Consumer Unit
The little box of fuses and switches that protects every 12V circuit in the van.