If you are having problems charging your vehicles battery or getting it to hold a charge there can be a number of reasons. If your batter is damaged internally because of perhaps a faulty or redundant cell it may well have had it and never really hold a full charge properly.
The other problem is if the charge of the battery is so low that it won’t charge properly. On some batteries if the charge gets really low they won’t charge without the use of a special type of battery charger.
It can be difficult to tell if a battery is accepting charge or not. A hydrometer is the best way to check this in a battery. But these days many battery’s are sealed and designed to be maintenance free so this isn’t an option.
The gauge on the battery charge can be used to check if a battery is accepting charge but this varies depending on the state of the battery and what level of charge it already has so is not always a straightforward measure of the state of the battery or charging.