Originally Posted by Ron101

Internal resistance will vary, good packs will be much lower and more uniform from cell to cell
I have been keeping an eye on I.R. for several years on my packs. I use FMA (cellpro and power lab) balance chargers they will tell you the I.R, while charging.

The other variable you will come across is the mah of the pack. What may be considered low I.R for a 2300mah pack would be high for a 8000 mah pack.

My thunder power 6s 65c 5000 mah packs started there life in the 1.2 mohm to 1.4 mohm range after about two years and many flights later they are pushing 1.7 to 1.9
These have been very good packs. They stay in very good balance before and after a flight

I've had a hyperion 6s 35c 6500 that was not staying in balance, the I.R. of a few cells was all over the place... might look like this
( 2.3, 4.5, 6.4, 2.4, 3, 2, 4.6) I would question whats going on with this pack along with the fact it's not staying balance... you may also notice the charger starting to stay in balance mode much longer at the end of a charge. Could indicate this pack is going bad.. I got rid of it

The best I.R. I have seen came for a recent batch of 6s 25c 8000 mah Nano Tech packs..... these are cheap packs from hobby king.
I'm seeing cells in the (.08 to 1.1) range they stay in perfect balance, very cool and come out of balance charge fast..... tells me there good cells

Now a smaller 3s 2300 mah pack may be considered good at 3 to 4 mohm .... if you see a cell hitting 7 mohm but the rest are down at 5 mohm and it's not staying in balance I would start to question that pack. If it was old I would get rid of it at that point.

I also mark the date on my packs if there getting to be 4 years old I'm about done with them... time to move them out. I used to mark cycles on the side of my packs but other than seeing how many cycles I got it really didn't help. I'm more interested in the balance and I.R., I like to look at the balance before and after every flight with my tester.
Check my I.R. every charge, just take a mental note and watch for something out of the ordinary. I find it kind of fun in some sick way...lol

For the record I buy expensive, cheap, and middle of the road packs mostly based on testing others have done. I've found bad cells in expensive brands and seen some of my best cells in very cheap packs. It's really hard to gauge... I will say the big name expensive brand packs seem to have better matching and consistency.
I bough a batch of cheap 6s 40c 5000 mah packs one was crap right out of the box, but the others were perfect and turned out to be some of the best cells I've owned

I take my old packs to our local household waste recycle center, they take them for free no matter what shape they are in
Watch those out of balance packs, any puffing or swelling and balance charge everytime