shoot, you got a GM, that thing will probualy hold a chrage for 2-3 months easy.
My POS Lambo wouldnt hold a charge for more than 5 days at its peak.
I would just goto WalMart and buy a charger/tender and just hook it up tp the battery post every once in a while then unhook it for several weeks. $20-30 should cover it. Dont even bother with the hard wired one that plug in. That for cars where the batteries are put in silly places like inside the wheel wells
or every 2-3 weeks on a sunny day with no salt take the car out for a short spin for exercise to just the fluids circulating and tires from flat spotting and oils up to temp. I do it in the winter atleast once or twice a month, for my mower too. It can be a chore, but it beats cleaning