Ageing battery
Batteries lose capacity with age and heat. A battery that tests weak under load will struggle on cold mornings or after the car sits for a few days.
Charging fault
If the alternator is not charging properly, the battery is never refilled while driving. A battery warning light, dimming headlights or electrical glitches while driving point here.
Parasitic drain
Something drawing power with the car off: a boot or glovebox light that stays on, an aftermarket accessory, a dash camera wired to a permanent feed, or a module that does not go to sleep. An auto electrician measures the drain and traces it.
Short trips
Lots of short trips with lights, wipers and air conditioning on may not give the battery enough time to recharge, especially on stop-start vehicles.
Safe to drive?
Usually safe to drive once started, but expect it may not restart. Get the battery and charging system tested.
General guidance only, not a diagnosis. If in doubt, do not drive it and have it inspected. In an emergency, call 111.
Who can help
Get quotes for car battery replacement near you
Questions
Will a battery charger fix it?
It recharges the battery but does not fix a charging fault or a drain.
Does my car need a special battery?
Stop-start vehicles usually need an AGM or EFB battery. Include your make, model and year in the job.