This will primarily be used to trim posts as they come off a pto powered post peeler so it will be really handy not having to start it so many times when I need to make a few short cuts.
I've seen two commercial makes of 12 volt chain saws over the years. But they are very hard to find. Maybe an appropriate sized starter motor could be used on a 120 volt saw in place of the original motor. Or just adapt a bar and gear to a 12 volt motor.
Even easier would be one of the battery saws. Sounds like it might be ideal for your use.
For example:
Stihl Battery Chainsaw
Forty minutes run time, about 3-5 seconds per cut...
Bruce