Campervan Leisure Battery Not Charging: Diagnosis and Fixes

A leisure battery that will not charge is one of the most common problems in campervan electrical systems. The fault is almost always one of a handful of causes. Here is how to diagnose it systematically.

First: confirm what is actually happening

Before troubleshooting, establish the baseline:

• What does your battery monitor show? (Voltage, state of charge)
• Is any charge source running? (Solar — is the sun out? Alternator — is the engine running? Hook-up — are you connected?)
• Has anything changed recently? (New battery, moved cables, recent fault)

Check battery voltage with a multimeter: probe the battery terminals directly, not the bus bar. Note the voltage.

Fault tree by charge source

Solar not charging the battery

Check 1: Is the sun out / panel unshaded? Obvious, but solar output drops to near zero in shade, heavy cloud, or parking under a tree.

Check 2: Solar charge controller — is it showing any input? Look at the controller display or connect via Bluetooth app. If it shows 0V input, either the panel is producing nothing or the connection between panel and controller is broken.

Check 3: Panel voltage at controller input Disconnect the panel from the controller. Measure panel voltage in full sun — should be above open-circuit voltage (typically 19–22V for a 100W 12V panel). If reading 0V, the panel is faulty, a fuse has blown, or a cable has disconnected.

Check 4: Controller to battery connection Measure voltage at the controller battery output terminals. If controller shows input from panels but battery voltage is not rising, check the cable from controller to battery — connector, fuse, and connections.

Check 5: Battery chemistry mismatch If you replaced an AGM with LiFePO4 but did not update the controller profile, the controller may be stopping charge too early (at 13.8V AGM float) instead of completing the LiFePO4 absorption at 14.4V. The battery appears "charged" but is only at 60%.

Alternator / DC-DC charger not charging

Check 1: Engine running? A DC-DC charger only charges when the engine runs. If you have ignition sense wired, it only charges when ignition is on.

Check 2: DC-DC charger — indicator light or app Most DC-DC chargers have an LED or app display. Check if it shows charging (output current > 0A). If it shows "off" or "standby" with the engine running, check the ignition sense wire connection.

Check 3: Input voltage at DC-DC charger Measure voltage at the charger's input positive terminal with engine running. Should be 13.8–14.4V. If below 12.8V, the connection to the starter battery is poor or there is a blown fuse on the input cable.

Check 4: Blown input fuse The inline fuse on the positive cable from starter battery to DC-DC charger input. If it has blown (the fuse wire is broken), replace with the correct rating.

Old split-charge relay systems: If you have a relay rather than a DC-DC charger, check relay operation — the relay should click closed when engine is running and the voltage exceeds ~13.0V.

Hook-up / mains charger not charging

Check 1: Is hook-up connected and the post live? Plug a lamp or phone charger into a 230V socket in the van — if nothing works, hook-up is either not connected, the post is off, or the RCD has tripped.

Check 2: RCD tripped Find your RCD (usually near the hook-up inlet or in a consumer unit). If the lever is in the middle or down position, it has tripped. Press to reset. If it immediately trips again, you have an earth fault on one of the 230V circuits — investigate before resetting again.

Check 3: Charger output fuse Check the inline fuse on the positive cable between charger and battery. Replace if blown.

Check 4: Charger profile / battery compatibility A lead-acid-only charger connected to a LiFePO4 battery may not charge correctly. Check the charger has a LiFePO4 mode and that it is selected.

Battery-specific issues

LiFePO4 in cold temperatures: The BMS disconnects charging below 0°C. If your battery has been in a cold environment, let it warm up (or use a self-heating battery). The BMS reconnects automatically above 5°C.

LiFePO4 deep sleep: If a LiFePO4 has been fully discharged and the BMS has disconnected, it may enter a low-power state where it does not immediately respond to a charger. Try connecting a known-working charger and leaving it for 10–15 minutes — some BMS units 'wake up' when they sense a charge voltage present.

Sulphated AGM: An AGM that has been left discharged for months may have sulphated plates. A charger will show charging current but the battery voltage does not rise properly. A desulphation cycle (some smart chargers have this) may help, but severe sulphation is permanent damage.

FAQ

My battery monitor shows 12.8V but no charge current is flowing. Is something wrong?

12.8V is approximately 50–60% state of charge for LiFePO4 (and 80–90% for AGM). At this voltage, a charge source would normally push current in. If no current is flowing, either no charge source is active, or the charge source is configured incorrectly (charging profile voltage is too low).

How do I know if my solar MPPT controller is faulty?

Bypass the controller — connect the panel directly to the battery (briefly, with a fuse) and check if voltage rises. If it does, the panels are working and the fault is in the controller. If not, the panels are the fault.

My new LiFePO4 battery shows 0V. Is it dead?

LiFePO4 batteries that arrive fully discharged or have been in storage may show 0V due to the BMS being in protection mode. Connect a compatible charger and leave it — the BMS may reconnect after detecting the charge source. Some manufacturers provide a 'wake-up' procedure in their documentation.