Strange start problem!
 

Im having some strange starting problems. Sometimes the car can sit for a month or two and will start right up other times it won't and I have to jump it I replaced the rear battery. Just now I went for a ride in it I had to jump it I drove it for like 20 miles on the interstate stopped to get gas and I had to jump it I'm not sure what's going on here when I got home I put a little trickle charger on the start (front) battery and it was green which means it's good. I checked it with a voltmeter and had 12.6 V I'm not sure if there's a sensor somewhere or relay that's causing problems any ideas?
I just went in the garage and now I had the red battery picture in the panel.
I tried starting it and it started right up??
I shut it down and tried starting it again and it started again???

strange start
 

what year model..?
im not sure but i dont think the red battery indicator shows up for the start (front ) battery... how old is start battery ?

05 SL600
Pulled the start battery and took it to Advance auto and had it tested.
It showed about 250 amps!

Purchased a new one from Advance that is a duplicate of the MB Battery.