I decided to go ahead with replacing my very dead Group 31 AGM batteries with LiFePO4 batteries of the same size. I contacted Smartbattery.com and they were very responsive to all my questions. They weren't the very cheapest I found on the Internet but they seemed to be one of the few who have a clear business and support their product. After a couple of days, I got handed off to their distributor in North Carolina who was also very responsive to all my questions and who went the extra mile in finding the correct answer for me and my specific set up. When I ordered them, I called the guy and gave him my credit card number on a Friday afternoon. I told him I didn’t need instant service and could wait until Monday. He had a different person call me for the details and I got the call back by 4pm which was too late for them to go out that day. But they went out on Monday and I got them via UPS on the following Wednesday. Very fast delivery.