Your problem is not the battery, but the charging system. The alternator should be putting out enough power to keep the lights brights and the other electrical items working. If the charging system does not put out enough power, the battery will be used to make up the loss. Eventually the battery power will be used up and the lights get dimmer, to the point that the battery is dead and so is your car (no engine, no lights, etc.)
Get the charging system sorted out and the battery problem will go away.
Bill
Vancouver, BC
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