On a couple of occasions even after a long run I have got back to the van to find battery completely flat. I bought the battery from Halfords just over a year ago. They tell me it tests OK. When I start the van the charge voltage across the battery is about 14.5V but sometimes there is a sound like ...

My 12v Waeco Coolmatic blew up on me last summer and I'm just getting round to replacing it. Couldn't believe it's going to cost me up to £650 for something I only use maybe 6 days a year. Can anyone suggest a cheaper replacement that won't be too much trouble to fit?