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Hey Guys, So my old group 27 batteries finally took a dump. I left the radio on in my truck for about 2 hours while I was loading up scrap, and it was enough that after starting the truck the batteries were just beyond this. Anyways, I did some quick looking and decided to upgrade to the famed Group31's. And the results are nothing less then amazing. So not only did the truck start up super fast, but even with the grids banging away the battery voltage went from 14.0 to 12.8V with the grids going off, and you don't even hear the change in the engine or the whine of the alternator, unlike with my old group27's Anyways here is how you do it. -------------------------------------------------------------------------------------------- Tools you will need. 1. A dremel or a drill with a drill bit. 2. A propane/ butane torch. 3. Battery Charger 4. Line wrenches for battery cables --------------------------------------------------------------------------------------------- Procedure 1. You pull your old batteries out. From here you will need a dremel, or a drill with a big drill bit. Either works good. 2. So first thing you need is to do is trim these notches off. If you don't the battery will not sit flat on the bottom of the tray, and this is crucial for the battery temp sensor to work correctly. And the other side 3. Start by heating up the battery box sides with a torch. Take your time, as it is better to go slow and steady then race this step. 3A You want to torch from end to end. 3B So when you torch one side so it is nice and warm and pliable, you swap to the other side, and then before you drop the battery in you re-hit the first side again for another 30-45 seconds then drop her in. To this end 4. Now torch away 5. Now after it is warm drop the battery in. 6. Let it cool down, and then pull it out. When your doing this you'll have to do this several times, its best to heat it up, and then drop it back in. 7. After each time you heat it up and drop the battery down you need to trim the plastic. Here you can see the plastic where its getting bigger. 8. Now its important to keep doing this until the battery sits on the bottom of the tray. This is the battery sensor, that my finger is on. 9. Hook up your batteries 9A. You may need to adjust the crossover cable between the two batteries in order to make the drivers side snug. 10. Use your 2/10/50 AMP battery charger to charge your batteries up. Once charged it works great. Some additional notes. 1. I had to adjust the slack on the crossover battery cable so I could get the drivers side positive terminal to fit on snug. 2. The battery hold downs do fit just fine, if you get the battery all of the way to floor. 3. There is about an inch of clearance between the top of the batteries and the hood. 4. Its best to charge your batteries until they are fully full before starting the truck for the first time. I'll update this with some videos in about a week when the weather turns. View full Cummins article