AGM Battery recomendations

[billschroeder5842]

Hey all!

Well my battery that I got on January 13 (karma) decided to belch out some acid fluid out the vent and onto my 91. I was lucky that I was just giving my car its weekly inspection when I noticed the fluid.

It sure could have been worse but fortunately, only a few wires are located under the battery. I cleaned up the drips, removed the battery tray and cleaned it mess with soap and water. I'll do one more tomorrow for good measure.

So.... I just got burned with a lead acid battery leak so I'd like to go with an AGM. I've just started my research and not finding too much that seems to fit C4s. I have an Optima AGM in my C5, but they don't seem to be making them anymore according to their web site.

Are there any recommendations for a AGM that will work well with our cars? I'd love to stop by a parts store tomorrow morning so I can take her out later.

I appreciate any suggestions-- Thanks!

[Matt B]

You might try an Optima Red Top 4.2. It's not quite AGM but their spiral cell stuff seals tight as a drum and has loads of starting power.
Only it HARDLY fits in our cars. You need to modify the battery tray to accommodate the larger footprint and ideally chop the positive pole off with a jigsaw. Otherwise in a crash it might get in touch with the piece of metal that runs over the battery.
All in all not the best option in terms of fit but a very good and safe battery that comes with GM correct connectors.

[billschroeder5842]

Thanks Matt, I'll look into it

[Hib Halverson]

There are few AGM batteries that will bolt right into a C4's battery location. Odyssey used to sell one. In fact, I had one when I owned "Barney" my '95 (SN 00140). Unfortunately EnerSys, parent of the "Odyssey" brand discontinued that battery.

A lot of the AGM batteries available now are not side-terminal only. They are "dual-terminal" batteries that are Group 75 or 86-sized but have top and side terminals. The problem with dual-terminal batteries and C4s is that the positive post is too close to the structural brace that runs from the firewall at the hood lock location down to the frame. As the car's structure flexes the battery moves up and down slightly and the brace moves around, too. it may end-up touching that brace. Once it touches the brace, the battery grounds causing a huge momentary short. Worse yet, if the battery mount or hold down is not tight or faulty and the battery moves touches that brace you get a big short.

The solution...cut the positive top post off the battery with a hack saw, jig saw or cutting wheel. Of course, that voids the warranty, but at least you'll have the best AGM battery on the market.

Since the early 2000s I have had Odysseys in all the Corvettes I have owned.

The battery that fits the C4 Corvette battery box is the ODP-AGM75 86 but you likely will have to cut the positive top post shorter.

[Mikey]

On my previous C4 I put a piece of rubber hose over the top post to prevent contact with the brace after I secured the battery with its tie down

[Matt B]

Here are a few pictures of my current battery. They say it's non spillable but it doesn't fit the ZR-1 without chopping off the positive pole. I also added a 0.15" layer of Teflon to the brace (not yet on the pictures).

You also have to modify the battery tray which I didn't. I first want to source a proper I replacement (anyone has an unmolested one on spare?).

One thing I realized AFTER cutting the positive pole is that its a two piece construction. The flat mount pole forms the outer layer whereas the inner piece goes into the battery. By chopping the pole the two pieces lose connection and in turn the flat mount pole is no longer energized. Pretty stupid, though... I used a soldering iron to fill the gap with solder and melt the two pieces of lead. Hope this lasts...20230220_112633.jpg20230220_112648.jpg20230220_112655.jpg20230220_112727.jpg