I'm experiencing issues with my two large D batteries. If I need to replace them, I'm considering using two Group 31 batteries in my 2002 MCI-D 4500. Does anyone have any advice on this? Thank you in advance!

Post by: Glennman

Post by: muldoonman

Group 31 batteries are half the size and half the juice.

Post by: Iceni John

Group 31s can have quite high CA/CCA ratings, but compared to 8Ds, they have much lower reserve capacity. If you live in a cold climate or at higher elevations, it could be a problem if you need to crank your engine a lot before it fires.   I changed from 8Ds to Group 31 batteries, but I can now also connect my house batteries to the start batteries to give me the same (or better) reserve capacity as the 8Ds I had before.

Post by: Glennman

Thanks, John. I plan to have them tested this week. I live in a cold climate, and we're surrounded by mountain passes. It looks like I'll be forking out a few more bucks, but the last thing I need is to have cranking problems in the cold.

Post by: Gary Hatt - Publisher BCM

I replaced my two 8D batteries with three Group 31s in my Eagle. The Group 31s are a fraction of the cost and are much easier to handle. I also had problems with my Interstate 8D batteries lasting only a couple of years before they stopped charging properly. The Group 31 batteries have lasted five years so far with no problems. 

Post by: dtcerrato 

We used to have shorter life spans with our 8D batteries until we upgraded our charging methods to four-stage charging; now we get eight or more years out of them. We retained the two 8D start batteries and have five Group 31 batteries in the house bank. All the batteries are hybrid deep-cycle and can be switched over for which bank serves what, including the inverter. It works great for us.

Post by: Dave5Cs 

Two Group 31 batteries are never a problem for me, even in the winter, which can get down to -30 degrees. They are a lot lighter and smaller. We also use a Delco 39MT starter, which takes less power. However, my Group 31's are 1200 CCA from Napa.

Post by: Glennman 

My 1974 MCI with the 8V71 engine has two group 31 batteries, and I've never had a problem with them even in the winter. However, they have been relocated to the rear engine compartment, as opposed to the side battery compartment. I figured that since the wires to the starter are shorter, it helped with the smaller batteries. 

Post by: dtcerrato 

In my opinion, if your engine is in good condition and starts quickly, even in below-freezing weather, one wouldn't notice a difference between group 31 and 8D. However, if there is ever a need for extended freezing cranking time, the basic difference would become apparent sooner rather than later.

Post by: Van

With a 24V system, two 8Ds or four group 31s are about the same. Either way, pay the money, then cry the blues in private like the rest of us. Don't forget to get a high-quality charger. I use Victron smart Bluetooth chargers, 24V for my four group 31 chassis batteries, and a 12V charger for my two 8D Lifeline house batteries, and one battery for my generator.

Post by: Gary Hatt - Publisher BCM 

My bus has wheels.  It never goes anyplace that gets below 40 degrees.  Just sayin'.

Post by: Glennman 

Thanks for all the help, everyone! As it turns out, one of my two 8D batteries has a bad cell, so I will be replacing just that one. I don't like having batteries of different ages used in pairs, but under the circumstances, I certainly won't be tossing a perfectly good one to satisfy my OCD.

Post by: luvrbus

Yes, with the 39MT starters, two more lawn batteries will start the series 60 in an MCI. With two group 31 batteries, you lose the reserve of the two 8D batteries. However, four group 31 batteries have about the same reserve, but this means more cables to manage.

Post by: Dave5Cs 

Nope, I lose nothing. Even when it is cold, it starts right up. My house batteries take care of everything else.

Post by: luvrbus 

Dave, you are starting a 426 CI, 6.6L engine. This guy has a 12.7L engine. Starting it takes a lot to get it turning. An 8V92 engine also requires some power to turn. The Series 60 doesn't pop off like a 2-stroke; they spin for a while. He made the right choice, but he will be buying the second 8D very shortly, because they are not going to equalize.

Post by: Van  

"Experience is what you get when you don't get what you need". I recommend replacing batteries as a set to ensure optimal performance.

Post by: dtcerrato 

Date codes are important too, as is with tires, just saying.