Madmouse said..
I bought a reasonably expensive Voltx battery and it was crap and didn't deliver anywhere near capacity. After a month or so I got my money back via PayPal.
Subsequently got one from China direct and it has been great. You need some simple/cheap capacity testing equipment and you need to know the brand of the BMS. I opened mine up to check but not by wrecking the case like Will does. If the BMS does not have Bluetooth you don't know what's going on so I would never buy one without Bluetooth. Not just a Bluetooth BMS that tells you basic parameters like average voltage overall but rather the voltage of each cell and hence the variance. A good bluetooth BMS should give you the full charging and error history;
ability to change a whole heap of parameters as well as forcing a top balance etc.
