Happened to me 2 weeks back. Was a couple of hours from seeing WG, but battery flat. Luckliy Green Flag were not too long, and offered me a new battery for £140. I declined and told him to tow me a mile up the road to the local motor factors, where a battery was £40. Got to the WGs on time, but just.
Made me think time to look for a new car given all the other faults.