So, I have had a Braille AGM battery in my sled for the last 3 years and over time it started to only hold a charge of 12.9v
enough to start the sled, but it was certainly slow cranking.
Here is a GREAT way to revive an AGM battery that you think may be toast!
First, I removed the battery and charged it with a standard 2/10/20 battery charger. sure it took a charge and the charger stated "FULL" but it only charges to 13.2v, not quite as much as the AGM full charge of 14.1v. so I attached a hi-beam 75w bulb and my dvm checking back once and a while to see when the voltage dropped to 9v. Once the voltage dropped to 9v I attached a "Sears Battery Minder" and let it float charge for a couple of days. Now the battery holds a full AGM charge of 13.9-14.1v for days!
Here's the interesting thing- when the battery minder was attached and the battery was at 12.5-13v it only would float the battery to 13.2, which would discharge within a day or so. However, after discharging the battery to 9v and allowing the "minder" to trickle charge the battery back to full voltage, it retains its full CCA! just to check the capacity of the battery, I jump started my BMW, with its battery dis-connected. After 2 revs it fired right up, and the sled had been sitting for 3 days without charging/running!
Long story short, dont ever throw away an AGM battery unless you are 100% sure it's bad!