Hi Neptune
The Headway LiFePO4 cells are good, but I am not sure I would buy them on ebay. I think you can probably get them cheaper from
BMSBattery but that depends on getting through customs without duty being added, as John said.
You can get the 16Ah version in the UK from
eclipsebikes @ £22.40 each plus postage. More expensive than China, but easier to get help in the UK rather than returns to China which is out of the question in reality.
in the last few years I have built two 39v batteries with Headway LiFePO4 cells. Both were using the slightly smaller 38120S 10Ah cells. The first set of 12 cells were originally in a battery pack I got from Cyclone TW about 4 years ago. I decided to dismantle the battery which had a built in BMS, as it was unreliable. So I did as you are suggesting, use an external balance charger or a bulk charge method and monitor cell voltage manually. This has worked well and the cells are still working although a couple are beginning to show signs of ageing, possibly the ones that had received an over voltage when the BMS that failed was in use.
The other battery is about 3 years old and I got the cells from
EV Assemble. Never used a BMS with these cells and they are still working well. The batteries are used on a system that peaks 2.5-3C(25-30A), but these cells are rated at 10C so can take this current peak with ease.
I have also used the same system as Jerry, making packs with the A123 2.3Ah cells. The A123’s are good for small compact pack building. And again I have made the batteries with no BMS built in. The A123 cells are very well matched and hold up better than the Headway cells.
Building batteries with no BMS built in, does mean that you have to do all the monitoring of cell balance and state of charge. But if you are willing to do that, then the other option would be to use RC Lipo cells which are the most powerful and lightest option for batteries, but unfortunately are the least safe if mistreated and their recharge longevity possible less than half that of LiFePO4.
Chris