First real test, I did this all on one battery charge. I only stopped when the motor started smoking a little (I changed a connector on the inside of the motor that had plastic that wasn’t high temp). This was over 3 feet deep at the start and tapers off to about a foot. Over a few weeks the sun has melted it a little so it was pretty tough. If I had shoveled it, I would have broken it off in chunks and just thrown them by hand.
But the snowblower just chewed it up! I’m really happy with the result! This might not win any awards, but it's enough for my needs.
If I get out there and snowblow the same day, I should be able to do all my driveways and sidewalks on one battery charge. That lets me slow charge the pack overnight with 70volts over 10 hours at 600mA. At that time / current / voltage there is no noticeable temperature increase in the batteries, so I assume most of the charge is going into the batteries. I don't think the batteries reach full charge, but they were designed to be between 40% and 80% most of the time so I don't need to charge to full peak.
Full disclosure, the motor does have some over-heating issues but I really pushed it's limits this time. I'll add a cooling fan, possibly some aluminum cooling fins, and call it done!