I have been storing cars for many many years and usually had at least 2 batteries dead and unable to hold a charge each spring... Since I started using  Battery Tenders' about 10 years ago I have NOT replaced a single battery in those ten years...heck most are warrented for 60 months and so I am well ahead of the game even though I paid between 30 & 40 bucks for each tender...

I do have battery cut offs in all the cars and ONLY turn on the Batteries when I want to drive a car...
Otherwise the batteries are cut off and usually hooked up to a trender... IF I know I will be driving one within a week or so I honestly do not hook a tender up to it...but it is winter and all of mine are now
in the garage until April Fools day (my oficial day to pull them out for the summer

Bob G.