Maybe its just how often I use my boats/jetskis but I never have to charge them, my speedster uses a full size battery then I am adding another as well, however the charging system charges the batteries so I guess with how much I use mine is why they never drain, Of course I am putting optima batteries in my boat though as well. If you let it sit alot then yes I would install battery tenders on board, you can also install solar chargers.