First,,,, have you checked to see that your voltage regulator is putting out the correct voltage?
Many people have had the voltage regulator go bad which ends up pumping the battery with excessive voltage (17-18volts) and cooking the battery. I would check this before going any further.
Second,,, the lithium batteries are known to have issues starting in cold conditions. And repeatedly trying to start the bike when the battery won't crank the engine damages them.
Just guessing here,,,,, but I think you damaged the battery trying to start the bike when cold. Possibly at the same time the voltage regulator is bad and the pop you heard was the battery from being overcharged. Like I said,,, just a guess.
You should post in this thread as he seems to know batteries very well.