Understanding, internal resistance on Lipo batteries?

[basher27]

From what I can understand, it sounds like the internal resistance is a good measure of a batteries health. I opened a brand new spectrum generation 2 battery and on its first charge It was getting a reading somewhere in the low to mid 2’s per Cell equaling a total of around 7 on my spectrum charger. I have an another battery which is the first generation spectrum battery with about 50 charges on it. And that internal resistance reading was in the low 1’s per cell totaling about 5. Am I missing something here? It seems to me the brand new battery pack should have the lowest reading. Thanks in advance as I’m trying to understand how this stuff works.

 

[Chapinb]

Don't total them together, each value is a measurment of that individual cell. There's an ir of the total pack as well, but thats not usually what we look at. This isnt the same resistance as a multi meter gets when youbmeasure ohms. The charger does some magic to measure resistance while charging. It's important to remember ir values change with charge state and vary charger to charger. An ir value on your charger might be 3 but on mine might be 2.5. Gives you a ballpark to compare to others, but it's not an absolute value.
The import bit is that they should be similar across all cells and hopfully across similar use/same make cells.
Ir is a broad measurment that shows you what the amp draw ability of the battery is - there's probably a rough equation or chart to infer ir to amp ability somewhere. If you track ir over time, you'll see it slowly increases. Meaning either the power delivery is lower or capacity is lower - which causes lower power delivery as well.
Lower the ir, the higher its ability to deliver amp. C rating and capacity should -should- be based on that or a similar, measurable metric like sag per amp draw... but alas...
So ir changes based on what it can deliver, that also means it changes based on capacity. 2 exact same construction lipo but one has double the capacity, they will have different ir - not necessarily half the ir.
So if the older lipo is larger, but used, I'd still expect a lower ir. A new lipo sometimes has a higher initial reading till its used a few times, then might settle into a stable ir. Make sure they were both measured at the same charge state - ir can change 10 fold empty to full.

 

[Dan B.]

If your cells on the other pack measure in the 1’s that’s fantastic. LiPo’s improve after being properly cycled a few times. Like @Chapinb said, the IR numbers are specific to each individual cell to monitor their health. You can have (and will at some point, I’m sure) a battery that has one cell showing a poor (high) IR rating while the other cells are good. Just keep running them and maintaining them properly and drive the wheels off them until it ain’t worth it any more.

 

[razorrc]

Batteries need to be broken in before they are performing at their best. I spend a few hours doing this actually…

 

[LibertyMKiii]

Like Razor said above use the new battery a few times and then test it.
Also temps make a massive difference. If one is 60f and the other is 85f then it wont be a fair comparison.