It was marked, sealed for life, I guess than when it "unsealed" itself, that was the end of its life!
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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 (I've charged it this way in the same place on the same charger for the last 2 years).
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