My truck is going to sit for at least 6 months maybe more will im gone on deployment. I know the computer and radio draw a little even while sitting and the batterys would be dead when i get home. I have never used a battery tender but i am thinking of getting one. Can they be used with two batterys and is it safe to leave unchecked for a long time. My batterys are 1 year old and my truck doesnt have any problem setting for 3-4 weeks but 6 months is too much. Whats my best bet.