Originally Posted by sacrifice

I have had a Polar for years and have had this problem occasionally. The problem is not the battery but the chest band. The instruction manual mentions (assuming they still provide manuals) that the band needs to be rinsed after every use and washed every couple of uses. This is accurate advice as I have found out by not washing the band. I now wash mine after every use with Dr Bonners hand soap and every few weeks put it in the washing machine with my wool laundry and use woolite (place it in a small laundry bag or a sock), and never have the problem, even with low batteries. The problem and solution has also been discussed on the Polar forums.