I own a 2gm20f as well, and learned a little about cold starting through experience. I took possession of the boat about 6 years ago in Maine
in October. On the start of my trip home, we had a couple of mornings with ice on the deck
, and I had real difficulty starting the engine
. Eventually I learned that it really likes to be on full throttle when starting in cold conditions. Totally makes the difference on my engine
... on a cold November morning I used to crank forever to start with throttle at idle, some reduction on half throttle, but with full throttle, it reliably starts in seconds. You may well be aware of this, but maybe it will help someone who was as naive as me.
btw, someone posted that 12.1v corresponds to 20-30% charge. I think that comes from room temperature data. Resting voltage is a function of temperature, dropping at cold temperatures. There may well have been a lot more charge in the OP's batteries if they were cold. Battery
meter is best, otherwise SOC estimation is just a wild guess without knowledge of battery
temperature and a cold-temp SOC vs voltage curve.