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 everything seems under control, you're simply not going fast enough" --Mario Andretti
1995 E500 street car
1986 Porsche 944 Turbo S track car