Peter, I think Tel is correct in a way, but I spect that a spark ignited the hydrogen someway. After all, they are usually charged at an even higher rate when used as starter batteries especially where there is an intake air heater like on Cummins diesels. I like the ones where you can remove the cell covers and check the water level as opposed to the "sealed for life" type. Just buy yourself a Dodge-Cummins diesel and you will have only the one heavy duty 12v battery to worry with. Jesse the crazed redneck machinist in Tennessee Not unusual Pete - unvented batteries and chargers don't mix - the generated hydrogen has nowhere to go but ..... It was marked, sealed for life, I guess than when it "unsealed" itself, that was the end of its life! http://www.lmandwr.co.uk/battery/battery_1.jpg http://www.lmandwr.co.uk/battery/battery_2.jpg More seriously, any ideas what could have happened? This is a battery that is used in my Landrover (in series with the "normal" battery) to give me 24v for the diesel heater. It comes out about once a month for charging. It was put on charge a couple of days earlier on a 12v, 5A (trickle) charge, I came into the workshop yesterday to find this! I have since charged a similar battery (same type) without any problems. Cheers Peter This email was cleaned by emailStripper, available for free from http://www.papercut.biz/emailStripper.htm MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.