As far as I know, they are OEM only. I've replaced a couple. I think the oldest was maybe 12 years old. (!) AGMs die a "sudden death." Fine until the next time, and they are dead as a doornail. We left a brewpub one rainy night in our 7 year old Prius. It started normally. When we came home, it didn't have enough power to do the shut down sequence. Fortunately, there is a place to jump them under the hood, and I used a motorcycle battery to do that, or I wouldn't have been able to open the trunk to get the dead battery out.