1C means 1 x the Ah rating of the cell. So for a 12Ah cell, dont use them at more than 12A, and theyll be at or under 1C.
2C is 2X the Ah rating.
On the site they say they can do 120Ah, which is 10C, which they claim is continous. But at the internal resistance they *actually* have (which is significantly higher than they say it is--which is a bad thing), the cells will waste a lot of power inside them, which heats them up (aging them faster, etc) and means you dont get all the charge in them out to your wheel, either. See the post I linked about that in the previous post.
As an example of how bad the resistance these celsl have is, in this post
viewtopic.php?f=14&t=81601&p=1200890&hi ... y#p1200890
Peter measured around 12-15 milliohm at half-charge (so call it an average) per cell. My entire EIG packs actual resistance (as measured by the Cycle Analyst during use, at all states of charge from full down to empty) is only 38 milliohm, and its 14 cells in series--so each cell is only 2.7 milliohm, or less than half of what he measured for the *full* charge resistance of a single Headway cell.
Mine are not the best cells you can get, either, by far, but theyre pretty good, and they came to me already used, so they mightve been better when they started out.
Anyway, as long as the current you need out of the Headway cells isnt too high, theyll work--but the higher the current you need, the worse the voltage drop will be, and the more heating of the cells will happen.