heavyMetal

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.

Metric Man

It might be the chest strap. They have a life span as well.

socalrider

I would double check and make sure that is the correct battery.. I have a 710 and 725 and they both use CR2354 batteries.. They are kind of tough to find and usually have to order online..

heavyMetal

The DL2025 was what was in the transmitter, and was working ok for the last year. I hand wash the strap after each use, but maybe it's finished. I got it at REI so maybe I'll bring it to them to see which component is causing the issue.

Not the Slowest

ummm, did you call Polar's TOLL FREE NUMBER, for customer service?

FYI, if you change the battery on your own, it can void the warranty.

heavyMetal

No, I didn't call them. Not sure how long the warranty is, but I've had it 3 yrs.

What I did do was ream out the contacts on the strap, and so far it seems to be working ok. There was a little bit of corrosion in there that I hadn't noticed before.

socalrider

Found my manual which covers the 710 and 720, it says:

Battery type: CR 2354

dfarinwi

Other posters may be on the right track, but it sounds like you caught a corrosion problem. T31 transmitters have an average life of 3 years and no replacement batteries. Sounds like you have a Wearlink transmitter with replaceable batteries though, and the straps are only around $10 if you aren't getting good contact any more. Sometimes, problems appear when the contact of the transmitter with the skin isn't the best. Usually, that goes away when people are sweaty or they use electrode gel. For women, an underwire brazzier can interfere as well.

Another possibility is radio frequency interference. Certain tail lights and flashing headlights have been reported to interfere with bike computer components, and the transmitter (chest strap) sends a radio frequency signal to your Polar 720i. The receivers (watch) seem to pick up radio frequency noise creating junk data from time to time in our cardio room and around our wifi ports. So if you added a new device recently, it could cause radio interference.

As far as changing batteries goes, no reason not to if you plan to keep the receiver dry, are careful not to strip the screws, and you use the correct battery type. Mostly, what you are paying Polar for is their technician's assurance that they place a fresh "O" ring and buttons lined up in the right positions so it remains water proof, and that they shouldn't strip your screws. That's especially important if you are a triathlete. At my school where we use downloadable Polar HR monitors for Physical Education classes, we change our batteries every year or so. It does void the warranty which I think is typically two years, so it may be worth paying for the first battery to be changed by Polar if you do it during that period. We never use them in the pool because chlorine kills technology even if it is designed for that kind of abuse.

dfarinwi

One other thought. Toss the strap in the washing machine with delicates (Cold, Cold). Don't put it in the dryer. I think they recommend doing this every month or so, and handwashing as you have been on a day to day basis.