Thanks okc329 and rjnonnie. The build date on the ML is 2/98 so the battery is almost five years old and probably near the end of its usable life. The weather here has just recently turned colder and no doubt the battery is struggling with the lower temperatures. I have been using Mobil 1 15W50 for the last six months since purchasing the vehicle. It may be better to switch to 0W40 for the winter months. Thanks again for the help.

Alex Lynch
1998 ML320 72,000 miles
1992 735i 249,000 miles
1986 635CSi 161,000 miles