Duralast GC2 battery Amp Hours?

The Xantrex inverter/charger that came on the boat when we bought it went up in flames (literally - didn't catch anything else on fire, thankfully!), and has been replaced with a new Magnum Energy inverter/charger. In order to properly set it up, I need to enter data about the batteries, so it can charge them properly.

The batteries are eight (8) Duralast Heavy Duty GC2 6 volts - pairs wired together make it four (4) 12V pairs. The only spec I can find about these batteries is on the label: "Reserve Capacity 100 Min." But from some research, it seems that a lot of GC2 batteries have a MUCH higher Reserve Capacity - as much a 400 minutes - so I'm wondering if this 100 Minutes on the label is giving me meaningful information (maybe it's at a different Amp draw than normal, or something).

I've sent emails to AutoZone (the retailer) and Johnson Controls (the manufacturer, I believe), but no response.

Does anyone have any suggestions for how I can determine the Amp Hours rating of these batteries? Is there some kind of test I can perform myself on one of them, to get at least some kind of ballpark rating? Thanks in advance for any help you can offer.

GC2 batteries as I recall have a slightly greater amphour rating than the more common GC batteries. So use 225 amphours for each battery. That will be in the ball park. Since you have 4 pairs, your total amphour capacity at 12V is about 900 amp hours.

The reserve capacity data is mostly useless for deep cycle use. The more typical spec is the number of amphours that the battery will produce when discharged over a 20 hour test period.

So this is what you can do to actually measure amphour capacity but it is tedious: Rig up enough DC loads to use 1/20 of the amphour capacity in amps or 45 amps in your case. You probably will have to hook up some AC loads to load up your inverter to pull this much DC current. Maybe an electric heater set to medium will work.

Then run that load for as long as it takes to run down the battery, theoretically 20 hours for a 900 amp hour bank. But if they run down in 15 hours then you have about 15*45= 675 amp hours of actual capacity.

But if your batteries are new, then 225 amphours per battery is within 10% of reality, probably on the high side.

David

David,

Something in your post made me Google some more search terms, and I found this on an RV forum:
Costco 6V Golf Cart Batteries... Specs? - Airstream Forums

Basically, according to the poster, the Reserve Capacity for GC2 batteries is calculated at a 75 amp load, instead of the 25 amp load used more commonly. He, too, said that GC2's are typically in the 200-225 amp hour range.

So thanks for the help in FINALLY figuring out this puzzle! I can now set up my new charger with confidence that I'm at least in the ballpark - even though I will probably never find the actual AH rating of my batteries. Score another one for Trawler Forum!

Follow-up: I finally got an email back from Autozone, which completely confirmed the above: the 100 minute Reserve Capacity is at a 75A discharge, and the C20 AH rating is 208. Thanks again, David, for your help!

Not meant to be a highjack, but I am also developing my house batteries to a 4 bank (8 battery) group of 6Vdc. Costco has Interstate batteries. Good? Is there only one battery or do the 6Vdc come in differant sizes?

Alaskan Sea-Duction said:

Not meant to be a highjack, but I am also developing my house batteries to a 4 bank (8 battery) group of 6Vdc. Costco has Interstate batteries. Good? Is there only one battery or do the 6Vdc come in differant sizes?

Click to expand...

Here is a link to Trojan's 6V battery listing. The T-105 (225AH) and T-125 (240AH) are the same overall size. The T-145 (260AH) is 7/8" taller. I'm not sure if other manufacturers offer the same sizes, but I suspect they would.

Alaskan Sea-Duction said:

Not meant to be a highjack, but I am also developing my house batteries to a 4 bank (8 battery) group of 6Vdc. Costco has Interstate batteries. Good? Is there only one battery or do the 6Vdc come in differant sizes?

Click to expand...

I'm pushing 4 years on my 6-battery GC bank without a problem. I found the Costco batteries to be the best bang for my buck. YMMV Also, they have a great return policy, if needed.

I believe the golf cart batteries are a standard size that allows 3 GCs into a single 8D battery box. Some may be taller than others, so I'd double check dimensions.