Most newer cars have a memory in their ECU so do not disconnect the battery without checking the proper reference manual for each vehicle.
Get a low low amperage float (or smart) charger. It will cycle on and off at certain battery levels. Some "trickle" chargers are just love amp chargers that send a small current of power all the time. As others have said, for peace of mind, avoid the HF unit. Lots of info here:
Battery Tender - Home of the Battery Tender Jr. - Batterytender.com
Setup the charger with the ring connections directly to the battery terminals (as opposed to the alligator clips) for a better connection.
If you're wanting to be uber safe, you can connect the charger to a GFCI wall outlet.
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Joe
See Porsche run. Run, Porsche, Run:
`87 911 Carrera