I assume you mean milliohms - 18 and 19 ohms would be huge for a lipo (even a NiMH). These are still big IRs even at mohms.

Seriously, I think you're seeing them age, poss normally for the lipo generation they come from (particular lipo chemical makeup). The other poss is that this is some slight accumulated damage and you've lost a small percentage of the media as far as it charging and discharging.

My IPs show 3mohms IR and my Neus show 2mohms, but they're young with less than 20cycles. Do you charge them fully after using and they then sit until the next use? I know we've discussed that's prob not the best thing to be doing for lipo life. Mine don't sit fully charged anymore, I've changed that.

You never really know how long these sat somewhere and this vintage or generation lipo was supposed to be good for about 2yrs and then head downhill due to aging of the media regardless of cycles. These are not date stamped, at least where we can see it, and that may be whats happening. Its hard to point at one factor and know for sure. I know you use good equip and don't abuse them, so it maybe something inherent to their vintage.