Killing a battery TWICE is definitely going to shorten it's life, but it's tough to say by how much. Since I use the same battery in both my 190 and MR2 (swap the cars and battery back and forth, 190 is "winter car", MR2 is "summer car"), I found that a Group 26R works fine as a replacement for the Gr. 47 in the Merc and Gr. 35 in the Deuce. Autozone sells 26Rs for 39.95. They are made by Johnson controls - same as the batteries at Pep Boys and Costco - just different labels, and have a 60 month warranty. I remove the labels and end up with a "plain black battery". For my conditions, these batteries typically last 7-8 years (if I don't severely discharge them), but they rarely see cold weather.