This question has come up a few times in the past weeks on how to install an AGM (Absorbed Glass Mat) battery into your dead acid filled Group 27 restoration battery. Originally I wrote up a little "how to" that was buried in the middle of another topic. I figured I'd make its own thread to possibly add to the tech archive.....

Basically, to gut the battery you need a large metal pail, baking soda, fresh water, long heavy rubber gloves, face shield, eye protection etc....

Small disclaimer....

YOU ARE DEALING WITH HIGHLY CORROSIVE BATTERY ACID
PROCEED AT YOUR OWN RISK
I TAKE NO RESPONSIBILITY FOR YOUR ACTIONS

I drilled holes at the bottom of the case to drain as much of the acid as possible. I work in a bus maintenance facility that has provisions for acid battery flushing & washing so this step was easy for me.

After thoroughly neutralizing the battery as much as possible (the glass matting will still hold acid) I figured I would try to cut a square out of the bottom of the case & all the guts would fall out....NOT!
The case is molded with plastic separators built into it to separate each cell.
I have heard others cutting the top of the battery off but I wanted to hide this battery as best as possible & I didn't want any potentially visible seams.
Secondly, the case is VERY thick plastic on the bottom & fairly thin on the sides. You have to be careful not to crack the side of the case when you are breaking out the plastic separators molded inside.
I used a whiz wheel for this along with a good dust mask because you WILL be black when you finish cutting the bottom out cell by cell.

Starting at one side of the case, after the bottom of the cell is cut out, each glass mat is separated by a lead plate which is attached to lead lugs at the top of the battery. There are aprox 6 lead plates & mats per cell. These have to be wiggled & broken off the lugs to remove. AGAIN WEAR HEAVY NEOPRENE ACID RESISTANT GLOVES!!

After removing all the plates & mats in one cell, break out the plastic separators, cut out the bottom of the next cell & move on till they are all out.
Wash out the case & then proceed to take out all the lead plate retaining lugs except for the 2 that the posts connect to. You have to take the others out to fit the new battery in the case. I used a Dremel tool with a small cut off wheel to cut through the lead.

Lastly drill out a hole in each post lug & make up some short battery cables to connect the new battery to.

Sorry I don't have any pics of the messy gutting procedure but here is a pic of the case that shows what I mean by the molded in separators & the lugs as well as the small battery cables I made ...



The battery I used was an Odyssey PC925
Odyssey batteries
....see the difference in size (also about 25lbs lighter)


Here is a close up of the post terminal & small cable.

You can see the molded in plastic separators I had to carefully break out with pliers etc....



I got 6 years 8 months out of my lead acid resto battery and it was still going (although it started dying if I didn't use the car for a week..that's why I did this....)
I have since added pieces of Styrofoam to take up the space in the case so the smaller battery doesn't flop around.


There's a tiny battery cranking that big bock 440 engine over? Where?





Hopefully this helps!


Chris

Great idea & write-up Chris! Do you know whether the battery you used will fit in a Group 24 case? I have some Group 24 cases that were reproduced in the 1980s that I would like to do this modification on...

Also, does anyone know where I could get the battery posts installed? The battery re-builders that I knew of are all shut down now...

With the top removed...

Great write-up Chris!!! You are quite handy and your write-up was extremely informative for all. Thanks Ron

Allen

It's a 27, the bottom came out because unlike you I had a sealed battery with plates & all the other nasty stuff to deal with... The battery only lasted a couple months & amazingly the battery posts still had lead rods attached that I was able to use.. Most guys seem to wind up tapping into the bottom of the battery post... Odyssey does offer other size batteries, a racer buddy uses their PC680 cause it's so small & light, fires his 12-1 C/R 440 every time, I like having as much battery as I can so I'd try to fit more but.... As I'm sure you know, this batteries can be placed in any orientation.. I think the 925 would fit in a similar fashion to mine, I didn't use all the space I had & I could have used considerably less...

http://www.odysseybatteries.com/batteries.htm

Here is what I will try to make work with the Group 24 case... My biggest concern is the 6 7/8 height when the battery is laid on it's side. Options would be going with a smaller/weaker battery, or cutting the bottom of the case out like Chris did...

So... Y'all think this might work? BTW, the bolt that the battery post adapter screws down on is welded to the power strap because there would not be access to keep the bolt from turning when the post adapters are tightened down. The final steps of assembly would be to set the pre-assembled battery with the power straps into the case, then place the battery case cover on the case, and finally install and tighten the two post adapters...

Here's another "favorite" thread. Thanks Chris.

No problem all....gotta give props where props are due....Randy (1_WILD_RT) was the one that gave me the idea in the first place

PS---Allen, I think your idea will work just fine....actually looks way over-engineered