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Coming up Hanwell today I happened to notice that my batteries (Domestic 4 x 110ah Numax sealed batteries) were charging at 34 to 40 amps (well that's what the gauge said). The voltage was 13.8. I thought that was odd as we had come from Kingston on Thames so that had given some time for the charge rate to settle down. Batteries are about three years old and are on constant trickle charge from a Solara 72 watt panel. I kept going down to check the charge rate which remained fairly constant at 34 peaking at around 40. There was a distinct smell of rotten eggs. I took the following action - please do let me know if there is anything else I should have done. Turned off the engine and switched off all the electrics bar the solar panel charging. The smell disappeared. Breasted up with my friend John and completed the flight and the trip to Bulls Bridge. Called RCR - they don't cover domestic electrics - should have read the fine print! When we got to Bulls bridge we looked at the batteries (easily accessible on my boat) and found two (furtherest from the Pos and Neg main cables) were very hot with the furtherest one the hottest. Now, some seven hours after switching off the charging to it, that battery is still very hot to the touch. There is no obvious external 'damage' to the two 'damaged' batteries - they look identical to the 'good' ones. The two hot batteries were isolated and charging returned to 'normal' - around 5 amps. The remaining two batteries were warm to the touch and appeared 'normal'. My questions are: Was the action I took correct? What could I have done to pre-empt the issue - i.e. could it have been detected prior to the failure - what maintenance should I have done that I clearly haven't because I assumed sealed meant sealed. The little windows all look the same - i.e. good. If I had left all four batteries connected and continued under my own power (i.e. still charging them) was there a danger of the batteries (or one of them) 'exploding'? Could the very high ambient temperature (up 30C) have influenced things. I intend to replace all four batteries tomorrow with new ones (oh dear more expense)! Thank you in advance for any advice.