LiPo cell resistance checker
Paste your cell resistances and see how far apart they are.
Why the spread and not the total
A pack's total internal resistance climbs as it ages, but on its own the figure says little: a shorty and a hard-case pack are not comparable, and neither are two chargers or the same pack warm and cold. What travels between all of those is how far apart the cells are. Every cell in a pack has done the same work, so one reading well above the others is that cell going first — and a pack is only as good as its worst cell.
So this compares the worst cell against the best as a percentage. Above 25% is worth watching; above 50% the pack has one cell that will sag under load long before the others, which is what a mid-final drop-off feels like.
Getting a reading worth comparing
Resistance depends on how the measurement was taken. The same pack reads far lower warm off the track than cold off the shelf, and two chargers will disagree with each other by more than the fade you are looking for. Measure the way you always measure — same charger, pack at the same sort of temperature — and the numbers start being a trend rather than noise.
This is guidance and not physics: chemistry, age and how hard a pack is run all move where the line sits. Treat a flagged cell as a reason to look, never as a verdict.