NRF52810 using CR2032 in freezing temps

Hello Nordic team, 

We have developed a smart tag using the NRF52810. We are looking at using it in asset monitoring application. 

It is powered by 2x cr2032 in parallel. 

My question:

1. Have your customers been able to power the nrf52 via cr2032 coin cell in freezing temperatures (-10 deg C)? Is there a better coin cell for this application. 

2. what would be a good capacitor size to ensure brown outs do not happen, given that BLE adverts take (~10ma for 380 us) x 3, while the CR2032 can only supply a 200ua current. 

The reason I ask is that I've tested 8 tags and they all fail in the freezer in 2 days. When I inspect the cell voltage, its at 1.5v or 1.6v. When I run the tags outside, they last months. I am assuming there was a brownout event, which pulled the mcu into reset which then discharged the cells. 

Kind regards,