Coincidentally Red Ken emailed me yesterday afternoon to tell me to connect a charger. You won't go wrong with the recommendation from @snrbrtsn. The Swedish company Ctek invented the concept of the smart charger and is certainly the market leader here in the UK. The 7 amp version is around £100 and the 5 amp version about £80 in Halfrauds. If you don't want to go out, Amazon is your friend.
I've always kept my 4 motorbikes on an Optimate smart charger and the perpetual monitoring and conditioning does prolong battery life by reducing the sulphation that ends up shorting the plates. My TVR is hooked up to an Ultimate Speed smart charger which was obtained from Lidl for the princely sum of £13.99 about 5 years ago. I can't fault it.
Red Ken is coming up to 4 years old soon and I suspect the original battery is now beginning to show its age. The Stop/Start hasn't functioned for over a year but I consider that a bonus. The battery capacity has been reduced because even using a tyre inflator via the auxilllary sockets causes power to be shut off within a minute or so as the sensor detects a significant voltage drop due to the current draw. A GLC replacement battery certainly doesn't come cheap, especially if the Stealer fits it.
many thanks for your reply! I THINK I see where you mean.