sensors

Hi,

I'm after some advice and hopefully someone might know the answer.

I have a polar V650 GPS head unit, I would like to get a speed and cadence sensor but from what I have been reading the sensors from polar are sealed units so if the battery is flat the sensor is no good and you have to buy a new sensor which I don't really want to do considering the price of these sensor. I did hear that some people had used the wahoo blue tooth sensors and they had connected and worked fine, does anyone have any idea or experience on this or is there any other sensors that may work, the polar only uses Bluetooth.

Thank you for reading