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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