Mio Go Watch manual - Mio Go Pedometer Watch Arctic

https://www.amazon.com/Stride-Heart-Rate-Monitor-Watch/dp/B001KYEYZW/ref=cm_cr_arp_d_product_top?ie=UTF8

here's the instruction manual http://help.mioglobal.com/hc/en-us/article_attachments/200504414/ClassicSelect_ENG.pdf

you will need to press the reset or a/c button located usually near the battery well with a pin and a magnifying glass

how do you get the battery out to change it?

Is your heart working? Sorry, bad joke. The only thing besides the watch malfunctioning is that you need to have your hand and arm relaxed when you touch the watch case. Apparently if your muscles are tense it can cause the monitor to not read.

mcdevito75 here, Most likely during the battery change you moved the quartz movement away from the contact buttons. Re-Open your watch carefully and make sure when you press the buttons, each button is pressing against it"s spot on the quartz movement.

Unfortunately MIO do not have repair services in Australia, probably would have to send it back to the US. Hopefully you can work with the seller to fix the issue. I know when you buy through mioglobal.com their customer service is excellent.

Have you contacted their customer service team? They are great at resolving issues and really stand behind their product. Their Facebook page MIOWatch also has lots of troubleshooting and FAQs too.

Use this link to download instructions for your Mio Sport watch:

http://www.miowatch.com/node/80

Do not forget to rate,please.

Yes, you definetely need battery replacement.
As the hart rate monitoring is most sophisticated part of the device, it has more IC (Integrated Circuits) than any other features.
More IC's means more power is needed, so, if the heart rate monitor is starting to malfunction, that's the very first sign of underpowered battery.
Find your nearest watch repair shop and ask for battery replacement.

Do not forget to rate, please.