tim macfarlane

While driving my 2007 alphard hybrid camper van conversion there was a loud bang and a steam like vapour was emitted from below the drivers seat. I took it to my toyota garage and they changed the main battery below the central console but didnt look at the auxilliary battery below the seat. I was able to drive home but after leaving the van for 5 days everything was dead and even a jump start to the main battery did nothing. I checked the auxilliary battery and found it hs only 5 volts left. I assume I will need to replace it with a new 12v AGM S55D23R-B 57Ah 430 A version. Does anyone know where I might get a replacement in London UK and whether when I refit it should I do further checks on the electrics. Here is a photo of the battery that failed