Can anyone tell me exactly what it is about Porsche electrical systems that causes battery failure after relatively short periods of inactivity? I had a 996 that was terrible - I used a maintainer all of the time to avoid problems. I have not had my 997 long enough to know, but searching this forum leads me to believe that I should stay with the maintainer. Most cars today have complex electical systems, alarms, computers, etc., and they don't seem to need such attention to the battery. My wife's Mercedes just sat for a month and started without any problem. What's the difference with Porsche? Thanks.

 

Unless the car is a daily driver, it needs to be on a maintainer, IMO. I'll give you a theory of what I think happens in my car. I drive my car once or twice a week. Sometimes I only drive it for 1/2 hour, on these trips. However, the car is sitting all week with all of it's gadgets "running" in the background. If my "short" drives once or twice a week don't put back 100% of the "juice" that was used during the week, there will be a deficit. In my opinion, this deficit is cumulative...so, it may take 6 months, 8 months, a year and a half, but at some point my battery will give me starting problems. Maybe the starting problem occured after a period of inactivity no longer than 2 weeks...so, my instinct tells me that my car died only after sitting for 2 weeks, which I think is crazy because other cars can sit for a month...when in fact the battery had been building a "deficit" over a period of months and the 2 week sit caused it to show up. Make sense? The bottom line, there is a difference in a daily driver sitting for a month and a weekly driver sitting for 2 weeks...because the weekly driver, if not driven long enough to make up for sitting for the week, will eventually run a battery down. All this being said, I put mine on a battery maintainer for a few days every other month or so. If the car runs at least once a week, it may not need to be on the maintainer but for a few days here and there to keep things on an even keel. Just my thoughts...

J

 

Porsche sports cars use moll batteries that suck big time when it comes to sitting. Additionally they are not sealed batteries so you need to make sure you check the levels with every oil change. When the car is off it takes about and hour and half to go to "sleep". At which time the current draw on the battery is typically 9-19 mA, max spec being 20 mA if I recall correctly. Recently I've seen a ton of 997s with melted starter/alt cables causing and under charge of the battery and occasionally damaging the alt. Fortunately that should be a warranty issue. Stick with the battery maintainer, and avoid using cheap battery shut off switches, and you should be fine.