I was measuring torque required to drive various drill bits and incidentally found that my cordless drill was delivering way less torque than it was spec'd for. 80in-lbs measured vs 250 spec'd. If this wasn't a Milwaukee drill, I would have dismissed it as a spooky torque spec. But 80 vs 250 for a Milwaukee doesn't figure.
The thought that came to me was maybe the battery couldn't deliver the current required for full torque. I tried 2 batteries, fully charged, and the results were the same. The batteries are 4-1/2 years old, but have only seen homeowner use, maybe a bit more.
So, my question is: do Li-ion batteries lose their current-delivery capacity with age? Note that I am NOT talking about capacity in its normal sense of amp-hours, but peak current.