I think you must have misread I put 1.2 milliohms per cell, so 2.4ish total on a 2 cell (I've never seen 0.5 milliohms per cell). I'm currently on the Team Powers 6600 in my 17.5 TC.

A cold battery will have higher IR (maybe around 3.6 ish per cell if you haven't used it in a while). So cycle at 40amps in the morning, run during practice charging at 40, and while waiting for your heat, cycle 40 amps at least once, more if you have time.

I got 1.2 + 1.4 on one on one of the TP 6600s that I've had since last summer. On a newish battery, I can get 0.9 per cell maybe lower but it's not really worth the trouble, probably deteriorates the cells a lot quicker, and usually involves technically being ROAR illegal (your battery cannot be more than 5 degrees over ambient).

If you use the battery through the race day, the IR should be the lowest right as you finishing your mains charge.

There are definitely safety concerns, probably wouldn't do any of this if you're just starting out. Use silicone 10awg charge leads bullets only. All connectors should have a tight fit. Don't use the cheap plastic wire or connectors since these will heat up and melt.