'But it was fine yesterday' — it usually was. Batteries rarely announce their death; they get pushed over a threshold by one of a short list of causes. Knowing which one hit you matters, because three of the seven will kill the next battery too if you only replace and drive on.
1. Something left on
Headlights, sidelights, an interior or boot light, a dashcam in parking mode. A single courtesy bulb can drain a small battery over a long day — ask anyone who spent eight hours at a château or an aquarium with the boot light on.
2. Parasitic drain
Alarms, trackers, dashcams and control modules sip current around the clock even with everything 'off'. A healthy car draws a trickle; add an aftermarket gadget or a module that never sleeps and a fortnight of parking becomes fatal. This is the airport long-stay classic.
3. Short-trip driving
Every start costs charge; only sustained driving repays it. A life of 2-km hops leaves the battery chronically undercharged, and a chronically undercharged battery sulphates — it permanently loses capacity. If this is your pattern, an occasional 45-minute run (or a mains charger) genuinely extends battery life.
4. Age
Past four or five years, the plates have simply worn. The first cold snap or the first long parking finds the weakness. No prevention here — just testing, so the failure happens on your schedule.
5. Heat — last summer's damage, this winter's breakdown
Heat evaporates electrolyte and accelerates plate corrosion. A Mediterranean summer quietly removes a chunk of capacity; the failure then shows up months later, on a cool morning, miles from where the damage was done.
6. Corroded or loose terminals
White-green fuzz on the posts or a clamp you can wiggle by hand: high resistance that mimics a dead battery. Sea air makes this a coastal speciality. Cleaning and tightening costs nothing — check twice a year.
7. It's not the battery — it's the charging
A failing alternator (or its belt) means the battery runs the car and never refills. The tell: a jump-start works, then the car dies again the same day. Replacing the battery 'fixes' this for 48 hours. This is exactly why we test the charging circuit before selling anyone a battery.
Whichever suspect got yours: if the car won't start somewhere in France right now, a technician can come to it, identify the actual cause at the car, and fix the right thing — in English.