sunclipper2000 Report post Posted August 31, 2018 I have a bank of 6 AGM batteries, that are going dead while in use, in about 45 minutes. They are 7 years old, so I am guessing they need replacement. Can I replace them a pair at a time, or do all 6 need to replaced at the same time. Thanks Share this post Link to post Share on other sites
wolfe10 Report post Posted August 31, 2018 sunclipper2000, Welcome to the FMCA Forum. Replacing part of a battery bank at a time is NOT recommended. Let's say one of the old batteries has or develops a bad cell, that 6 VDC battery is now 4 VDC. With it's "in series" partner, that is 10 VDC battery instead of 12 VDC. The charger will see low voltage on the battery bank and try to bring it up. That will well over-charge the good/new batteries in an attempt to being even the bad one up to fully charged voltage, materially shortening the new battery's life. Options: Save your money until you can replace all of them. Separate and load test the old ones and wire up only the good ones (yes in pairs) until you can replace all. Remove all old batteries and just install one new pair now-- OK if you don't do much dry camping. Add others as soon as you can so all are pretty close to the same age/kind. Share this post Link to post Share on other sites
manholt Report post Posted August 31, 2018 I think you have some dead cells already...I would load test them when fully charged...any Auto parts store will do. Share this post Link to post Share on other sites
dons2346 Report post Posted September 4, 2018 What brand are they? If they are Lifelines, there is a conditioning (equalizing) program that you can do with your inverter. Try that before you say they are bad. My Lifelines went 10 years before I replaced them Share this post Link to post Share on other sites
manholt Report post Posted September 4, 2018 Would your coach be a Gulf Stream? Share this post Link to post Share on other sites
