M5 Expert (>4000)
Join Date: Mar 2000
Location: Geyserville, CA, USA
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Interstate MTP-93 Replacement Battery - check your installation
My factory battery failed 6 months ago. (It was old, it was its time.) I replaced it with an Interstate MTP-93. A couple of days ago THAT battery up and quit - went from seeming perfect to not being able to turn the car over, overnight. I measured the voltage, it was 12.4. That should have been about 70% charged which should have been good enough to start the car, so I thought maybe I had a loose connection. Checked all those, all good. Tried again, no luck. Measured voltage again - this time it read 10.4. Aha! Shorted cell.
It happens. I'm not posting this to condemn the Interstate brand - it isn't a premium brand to be sure, but this is only one data point. However it is not a good one.
For a variety of reasons it was a lot easier for me to pull the battery and bum a ride to the local battery dealer than to jump the car and drive it there. I was lucky - the Interstate rep happened to be there when I pulled up. They put their own tester on the battery and proclaimed it dead, with a shorted cell, and they handed me a new one - the battery was within the 24 month full-exchange warranty. But the shop owner told me if the Interstate guy wasn't there they wouldn't have exchanged it - I would have had to bring the car in so they could confirm the charging system wasn't at fault. You are forewarned....
Important Installation issues: I didn't install the original 6 months ago, so I didn't notice this problem until I brought the new one home and installed it myself. I don't know if the new one is just a little shorter, or if the old one had the same problem - but basically, the battery actually sits about 3/8" too low in the battery box. This means when the positive cable is tightened, the battery is basically hanging from the metal arm that goes from the terminal clamp to the explosive cable connection. That puts a twisting torque on the battery terminal. This can't be good. Perhaps it was why my battery failed. (There were several cc's of battery acid in the bottom of the box.) If I had noticed this before I left the bad battery at the shop I would have reinspected it closely for cracks. When I installed the new one I put about 3/8" thick wood plate in the bottom to raise it up.
If you have this battery I would suggest checking this. It may be difficult to tell unless/until you disconnect the positive terminal from the battery - then you can see whether you can re-install it without it having to point down at a non-90 degree angle to the battery (bad) like mine.
Also, the "vent kit" is BARELY long enough (and maybe it isn't loong enough at all - time will tell) to stay seated in the rubber grommet that leads to outside the car. When I removed the old battery it was NOT sticking through that grommet. This could also explain why I had a little acid in my battery box. So while you're at it, inspect the vent tube too..... (I use a styrofoam block to keep the battery from shifting left and pinching the tube.) If mine comes out I will install an extension in the tubing.
Last edited by greg; 9th September 2006 at 12:08 AM.