We all make mistakes. 6.5 years doesn't have to be old for a battery, the stop-start not working when it should is the first sign that the battery voltage is low and the battery needs charging either by sufficient driving or the use of an appropriate battery charger maintainer following the instructions for the charger and those in the car's 'Owner's Manual' for charging. Occasional, or as required, preventative recharging of the battery will not only extended it's useful life but also possibly prevent unexpected various warning messages and lights, unseen error codes and electrical and running issues with the car that can be caused by the battery being too low for the computers to be happy and this is when the headlights seem bright enough and way, way before the engine doesn't start properly or at all. The battery has to be very low indeed for it to be unable to start the engine on a modern car. Loads of posts and threads on Briskoda for the modern models about low 12v battery issues. Of course some VW(Škoda) models can have their own issues with the stop/start working when it should, that's another matter, a few threads and posts on this but much, much rarer than the usual battery too low for stop/start operation when it should operate. But if the battery went as low as 2.5v last August and you've only just replaced it the battery must have been recharged (recharging to full 100% slowly would have been best technique to match drain situation) so that's not the cause of this electronic child lock warning. If the car isn't to be driven for 5-weeks best to disconnect the battery (as per 'Owners Manual') or leave the car on a battery charger maintainer then you could also leave the camera running if you want (subject to camera and other drains not be a very silly high voltage). If the AGM battery is in the engine compartment then it's supposed to have additional heat insulation over that provided for factory fit EFB battery but if you haven't tuned the engine up and/or drive like you might be on a racetrack then I'm sure it won't matter that much. I didn't add additional heat insulation and the AGM battery has lasted fine for over 4 years so far, but I do do occasional preventative charges to full and perhaps the AGM battery life has been shortened to what its full potential might have been but I expect it to take a few years more yet to find out. I expect the battery to outlast the car or our ownership of the car at least. So if you know for sure the child locks actually work (unless there's a fail-safe setting to remain locked) then you need to find out why the buttons don't light up when they should. Good luck.