Hey gang,
Just thought I'd pass this along...you would figure it out on your own eventually but to save time.
Had a TDA50 that after power cycling the phones would power on with "Incoming call xxx" on all LCD's and their msg lights would be on - system basically in "lock down" as well. Initialized and all would be fine until another power cycle test - found under Errors was Low Battery alert. Replaced battery and performed another initialization and all is well.
The battery (which is the same used in the old TVS 100,200 etc and many other Panasonic telecom equip) is CR2354-1GUF. The "1GUF" denotes the connector pin layout for the PCB connection - solders into PCB. I couldn't get solder residue completely out and replacement leads are squared...so had to do "custom" wire leads (phone wire) to battery leads etc..