Mazak nexus 510C II 52 battery alarm

Hello,

Can anybody help me to solve problem with mazak nexus 510C II milling machine?
Display shows error (52 battery alarm). We changed 2 batteries in NC block but problem not solved. Where is another battery? some says, another battery is behind display controler. I opened it but stlll not found. Perhaps I must look more carefuly? Can anybody give instruction how to find battery and change?
How to save nc parameters in usb if battery will drains totaly?

Sorry for my weak english

Sincerely,

Egidijus