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.
