Seems to me that you have to determine that the battery is getting fully charged while driving. Measuring the current into the battery and the battery voltage with the engine running will help.
Then finding out if there is a current drain from the battery when the engine is not running.
Then, if there is a current drain, determine what is causing the drain.
If there is no appreciable drain, the battery may be bad.
You may want someone who knows something about electricity to help you.
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