System fault

Unlocked the car this morning but it wouldn’t start. First of all, it displayed a ‘system fault’ message related to the car’s stop/start system, then that the electronic key wasn’t recognised. I changed the battery in the key to no avail. A Google search indicated that it may actually be related to the car battery.
In the end, after getting nowhere (literally!), I called out the AA. When he came out and did a diagnostic on the battery, it did confirm that it wasn’t sufficiently holding it’s charge. Fortunately the battery type was one that they stock on their vans, so he was able to replace it.
Am now mobile again, although my wallet is £235 lighter!