The way we figure battery life for a beacon with a coin cell battery is like this:

Based on the beacon broadcasting one protocol, interval of 1000ms, TX of 0dB, and set as unconnectable. 

CR20232 battery = 220mAh
80% available = 176mAh

176/0.0145/24/30 = 16.85 months. 

So we would expect this beacon to have a battery life of 16.84 months. To be conservative, we actually use 16 months as the promised number. 

The BC-U1 uses the same BLE radio as the above example (BC011) so you can expect it to have the same current draw (0.0145)

(the battery life would be about 15% less if the beacon is set as connectable, i.e. the current draw would be 15% more)