I've posted much of this elsewhere but I figured I'd update this thread too.
I purchased an Emma/Lau 48V/10Ah LiFePO4 battery in September '09 and used it for 38 cycles with not so much as a single glitch. My last ride of last season was on December 6th then the battery sat through the winter, though I did check the voltage regularly and top it off on occasion. Then one day checking the voltage I got nothing, nada, zero volts. I eventually found that the last cell group was low. I ripped the battery open, it was quite well built btw, and removed the two 5Ah cells which made up the last cell group. One of the cells was a lost cause but the other charged up to 3.35V, not that it's of any use to me.
I believe what happened is the rather fragile tab on the last cell, the one to which the main red lead was soldered, failed due to stress. Anyway the BMS would not work with 15 cells so off it came. I wanted to try a battery without a BMS I just didn't think I'd have the opportunity
so soon. My controller (21A peak) is well matched to the battery therefore I don't need a BMS to protect it from over-current and even at 93% DOD I didn't have a low-cell cut-off from the BMS so I don't really need that function either. In a way if you never have your BMS trip you probably don't need it. I did figure out how to jumper the BMS to use it as a balancer so it's still useful in that capacity however balancing of the cells isn't required very often.
I had a 240W charger on order from ecitypower because I blew up the original charger that came with the battery (don't ask
) but I ordered a 15 cell charger (Tenergy)from All-Battery just the same. They both ended up arriving on the same day. The Tenergy charger takes the pack up to 54.3V (3.62V/cell) which is perfect for every day charging. The charger from ecitypower was adjustable so I set it for 55.5V (3.70V/cell) for when I want to balance the pack with the old BMS.
I went for my first ride of the 2010 season on March 6th and for 6 cycles I dutifully recorded the individual cell voltages after a ride and after charging. After the first ride where I used 5.7AH all of the cells were within 0.01V. On the 5th ride I used 87% of the battery's theoretical capacity and the cells were still close though one cell I had already identified as a bit of a laggard was 0.04V lower than the average. After the 6th cycle I stopped recording the individual cell voltages as everything was looking good.
Without a BMS it's crucial to have closely matched cells and it appears mine are quite good in that respect. Since I mounted the controller on the seatpost I no longer have the Watts-Up meter in front of me to monitor the power use in real time though I do have it in the trunk bag for collecting trip totals. I wanted some kind of indicator so I purchased an LED headlight from China that has a few LED's on it to show the state of the battery.
It has 4 blue LED's which I found light at 43,45,47 and 49V and 1 red LED off to the left. As it turns out while it's not as good as being able to watch the WU meter it still gives valuable information. I can roughly tell how much current I'm using by how many LED's go out and once the "45V" LED goes out under load it's time to take it easy on the throttle and get home. I use the RED LED as a final warning kinda like the low gas light on my car. The earliest the red LED has blinked on was after using about 7Ah though if I'm easy on the throttle it may not come on even at 8Ah. This is about the maximum capacity I want to use, with or without a BMS, so it works out well. Oh yeah it has a nifty horn too (green button) which is handy on the bike path.
As of today (April 1st) I have put 17 cycles on the BMS-less pack and covered 507 miles and all is well. My top speed unassisted with 15 cells of course is down from about 23 mph to 21.5 mph and I do miss that at times however I usually ride at part throttle so it's not a huge issue.
Hmmm...I might just slide the 24V GM/Bafang motor core I have back in