Symptoms
Stop/start that works only sometimes or not at all, rough or slow restarts, low-voltage warnings and odd infotainment behaviour.
The fix, step by step
- Test the main battery first, since it is separate and a weak one also upsets stop/start.
- If the auxiliary battery is at fault, replace it with an AGM unit and register the new battery with a diagnostic tool so the battery-management system uses the right charging strategy.
- Check for any outstanding software updates.
Tools & part numbers
- Battery tester
- basic sockets
- LR047630 / LR176847 auxiliary battery
- diagnostic tool for BMS registration
Where to buy the parts
Hunting a used or discontinued part? Search eBay Motors for Land Rover Range Rover L405 parts →
Rated for a competent home mechanic with a decent tool kit. Confirm torque figures, fluids and procedures against the factory service manual for your VIN, support the truck on stands rather than a jack, and work at your own risk (disclaimer). Some parts links are affiliate links, which pay us a small commission at no cost to you.