Hi Dave,
I saw your #515 EEVBLOG, very interesting video. Do you have experience with those "Internal Battery Resistance Impedance Meter Testers" which you can buy from chinese websites e.g. Aliexpress. What exactly do they measure and are they trustworthy and useful? Maybe you could do a tear down of one those? kind regards,
hugo
They just load down the battery.
Real ones would test at 1kHz.