According to what I've read, overcharging LiFePO4 is not a big deal provided that you don't go too far. I have charged some cells to over 4v myself with no apparent detriment. Obviously,you should aim to keep them 3.65v or below. I've also read about some that were taken to 10v, which didn't catch fire or explode, but it can't have done them any good.
When you get/make a new battery pack, you've no idea whether you have any weak or otherwise defective cells, so you need to monitor their performance over the first few charges if running without a BMS.
Say you have a weak cell with less capacity than the others, and for simplicity, its a 10S1P pack of 36v of 5aH LMC. It wiil be 42v fully charged (4.2v per cell). Now, you use the pack,but one cell only has 3aH capacity. Your controller can only see the pack voltage, so when you've used 3 aH, the weak cell will reach its 3v limit, but the others will all be 3.6v or so, so the controller will see 35.4v and will keep going. If you continue to run, the weak cell will go down very rapidly into the danger zone until your controller sees a pack voltage of 31v or whatever, which means that the weak cell will be close to zero and the rest will be 3.44v,and you've used maybe 3.5aH. Confused by the lack of capacity, you put them on charge. Assuming that the dangerously low cell doesn't develop internal shorts and it accepts charge, your bulk charger will charge until the pack reaches 42v. The 9 cells will reach 4.2v after 3.5 aH is put in,but the weak cell will reach 4.2v after only 3 aH, so now it gets overcharged by nearly .5aH until the pack voltage reaches 42v. After over-discharging and then over-charging, there's a real risk of it catching fire. LiFePO4 is a bit safer from catching fire, but there's still a significant risk, like when that guy set his garage on fire recently when bulk-charging his BMS-less LiFePO4 battery that he bought from Ebay.
So, let's assume that your pack is OK. After a few charge/discharge cycles, where you've seen them all go up and down evenly by checking the cell voltages before and after charging with your bulk charger, you can take a reasonable risk of not checking them for a few cycles, and then gradually decrease the amount of checking. Obviously, if anything doesn't look right at any time, you need to check every cycle until you have confidence in the pack again.
It's not that you should balance-charge them for the first few cycles. You should use your bulk charger, but you need to check that they stay balanced,or you can use your balance charger, but you need to keep watching the cell voltages to check that they all go up evenly.
Monitoring to continue...
