I have two older Cadillacs with lots of electrical displays, gadgets. I don't drive these cars a lot and want to put both on a battery tender. I have been using a regular battery charger, but this allows the battery to lose charge when not connected, then fully recharge when connected, etc. I'd like to keep the battery constantly charged. Can you recommend what I need and where to find? There are so many of these chargers that I am not sure what to get. I would like to find one that does not require a lot of installation -- one I saw required a small box to be attached under the hood -- I would like to avoid this if possible. If there are models that attach directly to the terminals (easy connection and removal), I think those would be preferable. Thanks!