I drive my '93 600SL only on nice weekends. I want to keep the battery from running down when not in use, which can be for 2-3 weeks or longer. The Precision Auto Designs catalog includes 3 items, but I don't know which would be best. They sell: (1) a fused link battery switch for $19.95, which they claim is great for extended storage; (2) a Schumacher 1.5 amp charger for $34.95 that automatically switches on and off; and (3) a SureCharge II full floating charger for $34.95 that they claim cannot overcharge and can be left connected. I'm concerned about using either of those chargers with the negative terminal connected because the owner's manual says to disconnect it when charging the battery to avoid damaging other electrical components. Am I better off with just the fused switch? Or is the output of those chargers so small as to not cause any damage? If so, which charger would be best? Thanks for your advice.

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'93 600SL 20k miles