I know that the Interstate MTP-93 fits, but I'm not 100% certain that this definitively means it is group 93. I've also read that not everyone makes a group 93 battery but if you can find a 750-850CCA group 49 battery it should work fine too.

Any advice on this?

Why I'm asking:

I noticed on one trip to the gym last week that I thought the starter was cranking slow. Today I definitely noticed it, shut down in the driveway and pulled up the cluster voltage. With the ignition full on (ie. all the heaters, sensors, computers, DRLs powered) I was dropping into the 11s towards the 10s (it usually holds in high 11s with this load). When I cranked instead of seeing the usual spike into the 9s (when cold) the cluster went blank but it started and I saw 6.7V briefly when it came back on. Running voltage is 13.9-14.0 as soon as the alt kicked in.

Since the holidays it's been a lot of fairly short trips and I haven't been using my desulfating battery tender. I did pull the battery out of the car in Nov and check the electrolyte level and use a hydrometer to check the specific gravity. I was surprised to find my 5 year old battery showing 100% on the hydrometer - my factory battery at the same age showed 50%-75% and died (with the typical sulfation caused single cell short-circuit leading to a battery voltage of 10.4V) several months later.

Anyways, after driving for about 15mins on an errand with almost nothing optional turned on (have no choice about mirror heat, nozzle heat and drls) at shutdown the voltage stayed in the 13s and falling. On restart it dipped to the 10s and recovered to 13.9 when the alternator came online. I had about 15m more driving before arriving home. I put the battery on my 10A fast charger and it drew about 5A. In only 15min it was drawing significantly less and terminal voltage was up to 14.5. I switched to my battery tender since I don't want to puke acid all over my trunk by overcharging.

I'm thinking:

1/ Yes, I've been driving short trips, but some longer trips too

2/ Considering the depth of the voltage dips when starting, it should have charged longer and drawn the full 10A from my charger. Perhaps it's "worn out" but more evenly than I've killed a battery before.

3/ My hydrometer said it was still in great condition, but @#*(& happens I guess.

4/ Of course I don't know what rate the alternator was charging at while I was out. It is a 140A alternator. But, in that case, the short trips my wife has been making are similar and should have kept the battery topped up if my short trip was able to provide a significant recovery.

5/ I don't think I have the single failed cell death since 10.4 was not something I saw while testing and it recovered OK on the errand drive.

6/ Hopefully it's just low from short drives and high electrical load in the winter. It's not really cold right now (-6.5C) so that should not be a factor.

So, I want to start choosing a replacement and watch it closely for a week. I've read that JCI (Johnson Controls) is where it's at right now and I'd like to see if I can get a battery at Costco since the price and warranty can't be beat and the Kirklands are JCI last I checked. I'm pretty skeptical that they'll have vented Euro-size batteries but you never know and I'd like to have some equivalent group numbers on hand when I go. My Interstate still has some pro-rated warranty left but it would need to fail a load test removed from the car and that's a bit of a PITA with only one car just to get 10% off or something. I'll look into that too, though.

I'm happy with the performance of my Interstates but I'm not happy with their ability to keep electrolyte on the inside. My first (bought 2003) puked acid all over my trunk. Maybe from charging with the plug in charger, maybe from something else. My replacement for that one (free) will still show little droplets on the battery that aren't in one concentrated spot and any time I check my alternator is not overcharging. I've read similar comments online about Interstate MTPs so I don't think it's just me. Of course I think Interstate might also be JCI so....

I had heard good things about Deka 10 years ago - nothing but bad stories now. Exide seems to have a bad rep for rapid cell short failure and leaking too. I'm not going to put an Optima in there with spit and bailing wire. The dealer batteries are just too expensive. There's only so many people who actually make batteries...