Hi Gareth,
The replacement I've ordered is a Bosch S5A08 from batterymegastore.co.uk
When ordering I entered the registration and was then given the option 'does your car have a start stop system' to which I selected yes, all the results then came back as AGM batteries.
In the vehicle handbook it states 'your vehicle is equipped with an intelligent power system to control the distribution of electrical energy. It also states vehicles with e.g start stop system are equipped with a special deep cycle battery (AGM type). The on board electronic systems may develop problems if you fit a different type of battery.
So hopefully, the problems have been down to the old battery not being compatible?
Kind regards,
BP