And I will take the other side..I say it is more than enough. I have a Cummins in a 91 truck, and it has a single battery as stock. I have been using an optima red top and it's been in the truck for 4 years starting in the CT winters and summers. Every Cummins B series I am familiar with always starts on the first couple of compression strokes. Jay My guess is that's cutting it too close. I use a pair of the smaller, lighter, and less expensive Optima red tops in my Cummins 5.9 ISB pickup, and two 34M blue top starting batteries (each 800 CCA, 1000 MCA, same as red top except for the terminal type) for my boat's Volvo KAD44. A pair weighs only 77 lbs. Richard Cook New Moon (Bounty 257) John Wix wrote: > The owner's manual for my Cummins 6BT5.9M states that 950 CCA are needed for > starting. The Optima D31M has 900 CCA and 1150 MCA. Is that cutting it too > close? I like the compactness of the Optima, but I don't want to be "on the > edge." Jay Leonard (860) 945-5456 1-800-775-2690 ext 5456 FAX (860) 945-5403 jay.leonard@timken.com ----------------------------------------- This message and any attachments are intended for the individual or entity named above. If you are not the intended recipient, please do not forward, copy, print, use or disclose this communication to others; also please notify the sender by replying to this message, and then delete it from your system. The Timken Company / The Timken Corporation