Just starting their sixth year probably replace next spring. Just replaced the starting batteries after nursing them along these last four months. They almost failed to start the diesel when breaking camp last Sunday. Has at least one bad cell. Upset DW a bit when I wouldn't stop on the way home for shopping as I was afraid she wouldn't start again.
Hearing the motor start in two seconds versus listening to the starter crank slower and slower before finally starting is very comforting.