IF you are worried about recharging a low battery with just your alternator, Get a good battery charger and hook it up to the jumper point in the engine bay over night. Make sure the charger is designed to slowly charge the battery and cut off when the battery is topped up.

BTW whenever you don't drive your X5 for weeks (or months) you should put it on a trickle charger to keep your battery from going flat. Modern vehicles don't handle dead batteries gracefully.

Funf Dreisig