Charge AGM battery

Hi guys, my new Golf Variant has only been on short distances lately and there are currently no more than 30km of rides available. When I used the same thing with my Audi, it didn’t start in the winter of one day – battery is empty. I think this is even worse with the current car, because the Audi had no start-stop system. Now I have two questions: a) Does it make sense to charge the battery with a charger? b) Can I use a “normal” load for this? Have the OXFORD Maximiser 360T here. Otherwise I have a high-end charger here, where I can determine all parameters myself. I would not like to take the device outside.