Okay, say you rec'd a hardcase lipo, with no decal or mah info whatsoever. Is there a way to determine what the pack size is?

Cell count can be determined by the balance plug. Set your ESC and run it (carefully) down to 3.2V/cell. Top it up and check the charger to determine the approximate capacity. No way to check C-rating though, so I would reserve the pack for testing instead of bashing or racing.

You're also gonna have to guess at what to charge it at....

open up the case and look at what the bag says it is.

I know its a 2s, so my question is mostly centered around mah-4000? or more, so I know where to charge it. I thought maybe with all these fancy gadgets I see advertised here and there one could measure the capacity somehow..May just charge @4.0 and see if it takes it all, then 4.5 and so on.

The cells I've looked at either repairing or attempting to repair have had some capacity info posted on them. I agree with Tim - just hope you can read the info, seems like some get assembled before the info has had a chance to dry...

Dimensions and weight (in addition to what is stated above) would go a long way in determining the capacity and specs. Beyond that you might find someone with a CBA and amplifier to generate graphs and be able to "call it what it is"

I've re-labeled a number of my packs with true numbers. I'm sure with just a few tests one could match it up in the battery graph vault. If you don't find a local one I would be willing to test it for you , and I thing the CBA even has label printing capability.

Alright, thanks for the info everyone..