Cheap way to measure capacity? You can get a rough estimate by measuring current draw in milliamps on a flashlight at a regular intervals like 10 minutes until you get down to whatever cutoff voltage you want. 10 minutes is 1/6th of an hour, so you total all of the current readings and divide by 6 to get mAh. You will have to average the initial and final reading or you will have one reading too many.
If you get a hobby charger you can do it, but mine will only do a maximum discharge rate of 1000 mA.
I have some of the Trustfire 3000 that I bought a few months ago. They seem to be good and hold more capacity than my other less expensive batteries. I just ordered 8 more from MF the other day. I hadn't heard that some are having problems with newer batches. Hope mine will be ok.
I recently bought some 2900mah unprotected panasonic NCRs from focalprice. I think they are ~$7.50 shipped. If you buy more than 3, then it starts getting cheaper. I just received it the other day... running some tests on them and will start another thread and report back when done. But here are a few quick figures for you:
-arrive at ~3.64V
-charged up to ~4.16V
-Discharged at 200ma, until it reaches 3.0V (low cut off for my acucell 6). Gave 2749mah. Resting voltage after test 3.19V (this means there's still juice left in the battery, as the ncr18650 can be discharged to 2.5/2.75V).
My only concern with these batteries are the middle of the battery bulges out very slightly. Probably not a good sign?
I don't think it will show up very well on photos.. it's hard to see, more a tactile thing for me. I'll try post some photos when I get a chance anyway
Try using a caliper to measure the difference , diameter towards the ends and diameter on the bump. Also you can check later if the "bump" diameter has increase with use or not.
Not sure about MarsFire ones, but intl-outdoor carries unprotected 2600mAh Sanyo's for $1.5 less: http://www.intl-outdoor.com/sanyo-18650-2600mah-liion-battery-p-135.html