I thought the issue with the Merc EFI stators was that you could be at risk for burning up the voltage regulator or stator? I don't doubt that it could shorten battery life as well, based on what they've said over there on the Merc forum - I have no personal experience though. Oddly, a bunch of people with similar vintage Yammie EFIs and stator charging systems have had a good, long life out of AGMs, so something must be different.