Complete Engine cut out

[JPGStewart]

First time post! I have a 2017 S Class 500 Convertible........its only done 11,000 miles from new and has been no trouble until the other day. I was
doing 20mph in slow traffic when the engine went dead and all electrics cut out. Nothing worked, even the central locking and couldn't open the boot
using the key fob. It was as though the battery had been disconnected!
Two hours later the car started fine and has run fine since. My local specialist plugged in the diagnostics and said the battery was very low and might
need replacing [the main dealer quoted £1050 for a new battery....not including fitting!!!!......is this a record?]
Has anyone else had this issue with the 500 engine. Should I be worried?

 

[zipdip]

Well I take it your car has two batteries,because the starter battery for you car is around £200 or less, my S much older than yours has two batteries,but then later they only used one,now it seems your car just 3 years old and a W222 convertible has two I suppose given the roof has to go in the boot the battery will be under the boot floor somewhere,have you looked in your manual.