I am having this same exact problem and am trying to figure it out. With your priority start I would think that your battery would continue to be drained and recharged every time you start and use it, wouldnt that make the battery only have a limited life? I would rather fix this where I did not need an aftermarket device.

It is a 96 SL500.

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2007 Corvette Convertible Torch Red
1996 MBz SL500
2008 Harley Davidson Night Rod Special