Take the battery out. Put it in reversed for a few seconds. Take it out, then put in the right way.

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Trust me I’m a doctor!
Well, I have a PhD :-)

Tried it, still doesn't work. Should I just get a new one?

Maybe a dumb question, but are you wearing it when you try to discover it? If yes, then it's dead. I seemed to have to replace mine every 1-2 years.

Same thing happened to me. Only mine lasted 2 years. I’m guessing it’s dead. I’ve tried everything. I think over time with the sweat and water it just conks out.

My HRM-Run has been funny as of late. A couple observations, it seems to burn through batteries as compared to the original one. Recently I thought mine was dead too and I pulled the battery out and left it out for a day, then put a new battery in and it's working again.

Overall I'm not a fan of the contacts, housings, etc with these coin cell batteries we use in our HRM, bike computers, PMs, etc.