2015 Civic EX 4 dr w CVT. Car consistently started well recent during cold snap (minus 20 C overnight). Roughly 80% stop & go / 20 % freeway driving. After five short hops and normal starts, took veh. for 20 mile drive at 60 mph. Radio was on during most stops. Shut car off, went in to pick up coffee, radio on. Car refused to start. Barely a flicker on dash lights. Required boost and has run fine since. Apparently Honda sets up 9th Gen. computer to tell the alternator to reduce charging, and this often leads eventually to completely dead battery? Am I correct? Would installing analogue amperage and volt gauges help detect problem before battery dies? Dealer wants to sell small add-on dodad that fits to battery that supposedly keeps battery working. Not sure how that would work. Local mechanic suggests small trickle charger with over load protection - great idea - but then I need a hundred foot extension cable from 2nd floor aptm. to car. Unlike Edmonton, AB or Winnipeg, MB, Nova Scotia does not normally provide plug-in posts for all parking spaces. This is potentially seriousness problem as the winter gets cold here, not everywhere has cell coverage, and somehow I find this idea of setting up a car to have an intentional parasitic drag downright stupid. We love our Honda Civic. Great highway cruiser. The last resort will be to fit a bayonet switch into the ground cable to isolate the battery when parked. Canada needs your
HELP!

 

How old is the battery? Before buying anything, I'd have it checked. It's free at a lot of parts stores, at least here in the US.

 

Can't get near the battery at the moment w/o removing cables and cover to find the date of installation on battery. The terminals could use a cleaning. And the voltage measures 12.6 volts across the terminals - not good. After 27 miles of 55 to 70 mph four hrs ago. Snowing at the moment with a north wind. Will clean terminals tomorrow and confirm install date. You may be correct as to a new battery. Still doesn't answer the question about so called smart alternators on 9th Gen Hondas. Apparently this is an industry wide trend to boost fuel mileage. I'll post after confirming a few things.

 

At the beginning of a battery's life, 13.0-13.2 is pretty common, but at it's mid life, 12.6 is very common. 12.1 is when I prepare for a new battery; in past experience, 12.1 volts means I have 1-7 days before it conks out. Now, if you're getting 12.6 while the engine is running, then you have a charging problem.

A test I do is I check the battery voltage at night before bed. Then, I check it in the morning to see if there was a voltage drop; 0.1 - 0.3 volts is okay; 0.4-0.5 and I probably have a dying or dead cell. I also check it while the engine is running to make sure my charging system works. 13.2-13.6 volts while the engine is running has been pretty standard, IME.

 

2015, probably the original battery. Your extreme low temperature is going to be hard on even a healthy battery. I would look at battery replacement. Doubtful it is a charging system issue.