I'm having similar problems since I went to Coventry.
Can someone advise where to find the 12v battery?
Also, does the infotainment system require a PIN when it restarts after this process?
Battery is easy.
Open the bonnet, look in the right side of the engine compartment, can't miss it.
No, the radio needs no code, this is something that was used in "the old days" when radio's were all DIN sized and could easily be stolen.
Nowadays the infotainment computer is fitted under the dash and usually coded into the car, so even if someone stole it, it would not work in another unit.
They claim the reason they "lock" each unit to a specific car is to prevent theft, but in reality they do it to prevent someone with a defective infotainment ECU from going to the scrappers and just getting one from a wrecked car.
This way, your only option is to buy a new one and have it fitted by them...The used units can not be reset, they claim....Of course to prevent thieves from resetting them and selling them on the black market.....But again, obviously because they want to sell a new unit, rather than recode a used one.