HRM-PRO looses connection after and can t recover it again

Hi,

I used to train with hrm-pro for a couple o years. Then I removed the battery and I kept it in a dry and safe place for three months. Today I decided to use it again and I mouted a new battery..

Connection can t be established!!!

I tried a factory reset by placing the battery swapping + and -. This makes the sensor working only for some minutes.. then the connection is lost again and can be recovered only with another reset but again only for some minutes... and so on.

I tried ant+ and BLE. Still not working.

Any ideas?

Thanks