If you have half an A main full of drivers with lap averages top 5,10, and 20 within a tenth or so on a wintertime carpet track with cool temps, it can make a difference. At a COLD carpet NATS with a tech table near a door, rumor has it you could charge at 40 amps and pack would be cold by the time you got to the top of the line in tech.
They stopped temping packs, probably because the tech area was so cold it didn't matter.
All I can tell you, most of the fastest guys were coming to tech at the last possible moments. My guess is to keep some heat in the packs.
But at a NATS, you'll do almost anything to get those last couple 100ths of a second. Since the ambient temp at the tech area was 50 degrees, I'm sure the potential gain was slightly magnified..
On a club level, charge at 8 amps and don't bother ruining good packs...