Central locking/ignition cut out via fob 2 of 2 probs

Fitted new regulator to TT and flattened battery getting window in right place.

Charged battery in situ with car unlocked but all connected. Got in it to take to respray and fob no longer works. Ignition needs to be turned on via “two pin fob” and key works central locking.

Have I blown fuse/relay for fob receiver or something or has 30 year old battery in it gone flat lol. Help should have two cars nearly perfect and both let me down today ,albeit both drive perfectly.