The Polar T31 chest strap transmits your heart rate to a Polar heart rate wrist unit. The slim band reads electrocardiograms (ECGs), providing you with an accurate heart rate reading during training. Although newer models, including the Wearlink 31, have rechargeable batteries, the T31 model has a battery life of 2,500 hours or five years of use. After that, you will have to have the battery replaced. The transmitter is sealed because it is certified for swimming. This means you will not be able to open up the chest strap to replace the battery yourself, and you must return it to the company for battery replacement.
Test your transmitter indoors, in a cool, dry location. Often, cold or damp weather can hinder the operation of batteries.
Find your closest Polar service centre from the ones listed on the Polar USA website. (See Resources)
Click on the "RepairReturnForm" PDF link on the site. Fill out the form. Because batteries are not covered by the product warranty, the online warranty forms will not apply to you. Pack you device carefully for shipment.
Send your forms along with your chest strap to your closest dealer. Include your credit card information on the forms for easy payment of parts replacements and return shipping and handling.
Wait at least seven business days for Polar to replace the battery and ship it back to you.
Keep your unit dry. Wipe off any moisture after each use.
Keep your unit out of extreme heat or cold. Do not store your unit in a plastic bag.