@josb, thanks for the feedback. As I indicated, I don't actually own the Scubapro HRM but over the years I have collected a variety of HRM's for my training. The diagram in the manual isn't that clear so I attached a photo with two different designs. If the battery sits within the cap, then something like a paper washer or small o-ring to sit between the cap and battery may elevate it enough to apply more pressure to the contacts. But if the cap just presses down on the battery then I suspect it may be the positive contact that is on the side of the well which needs to be bent a little to make a better contact. Then again it may be the PCB in the unit itself where pressure distorts the board and breaks the circuit. If this is the problem then the unit needs to be replaced. But @Hatul indicated that he was able to resolve the problem by replacing the battery so I still think its a simple battery contact issue under pressure. Of course if the HRM is still under warranty, then send it back to Scubapro and have them fix the problem.