A battery that goes flat and stays flat for days loses some capacity for good, because hard sulphate crystals form on the plates. One deep discharge is usually survivable. Three or four over a summer are not. That is why a car driven hard at the Autodrome once a month can need a battery sooner than a taxi that never stops.
Modified cars add to the load. Aftermarket audio, trackers and dashcams in parking mode all draw current with the engine off. If a battery that tests healthy keeps going flat, something is draining it, and that needs tracing in a workshop. We can book that for you through the same WhatsApp number, with pickup from Motor City.