I've got a Polar 720i with speed, cadence and HRM sensors. The other day the HRM was showing weird values, like 00 and 222, so I replaced the battery (DL2025). Today I went for a ride, and the HRM was reading 226 as soon as I got on the bike. It was all over the place on the ride, so the battery replacement wasn't the answer. Anyone know how to fix this, or do I need to get a replacement? I've had it for 3 years, so it's probably out of warranty.