Agree with MB Doc; been there with my '88 300TE. When my battery went south, I was in the process of replacing it when I found the battery tray to be corroding. I ordered a new OE tray from the dealer, and the only one available would fit either size battery. So, after a little homework and the recognition that there's no downside to a bigger battery other than weight and a marginally heftier price tag, I popped for a humongo battery. I simply don't do battery-related breakdowns, and I live in the frozen Northeast.

Buy the best battery that you can, and forget about it for about 6-7 years.

Best of luck.

__________________
"If God had meant for us to walk, why did he give us feet that fit car pedals?" Sir Sterling Moss

Michael
2014 E63S Estate
2006 SLK55
1995 E500
1986 Porsche 944 turbo