So the battery on the F finally gave up the ghost, I did notice over the last few weeks slow crank on startup.
On inspection turns out its the original battery ! so its done well to last 10 years. Removed the battery turns out its made by Panasonic.
After a quick measure up sourced a replacement from Tayna online. The battery they have listed on their site for the ISF is incorrect, it will not fit as its too long. The correct size battery is the one they have listed under the IS250 https://www.tayna.co.uk/car-batteries/enduroline/069/
Fitment was straight forward, the battery fits perfectly, and the plastic casing which goes round the OE battery fits perfectly over this battery. The only slight variation are the terminals are situated on the front of the battery not the rear. Not much difference, and the cables are long enough to fit nicely. Just needed one of the clips on the positive wire moving along a few centimeters to clip on the battery case housing.
Car cranks over much better now so job done.
Took 15 mins.