What is wrong with car battery?

My car battery ( which is only 18 months old) does not hold a charge. I rarely use the car, and recently I have had the battery on trickle charge for 12 hours a day. When I disconnect the charger, I can manually start the car. However, when I try the starter the following morning ithe battery seems dead. I checked that no electrical item was left on at night but all seems OK. Surely I do not need a replacement battery yet! Hyundai Coupe by the way.
David Ball, July 2020


done
Is the car charging the battery OK? (The voltage across the battery should be about 14.4 volts from memory, with the engine running and once that battery has absorbed enough charge)

Have you checked with a current meter what the actual drain on the battery is, with everything switched off? It won't be zero if there is an alarm or something like that fitted, so a few milliamps should be neither here nor there

Fghsj, July 2020
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