I have made my own batteries out of A123 18650 cells. Works great for me. I have no bms or any safety measures. I just pick out of a pile of cells and check the internal resistance of the cells and group them accordingly. I have done around 6k miles (7months) on my last battery which is just a 4s4p (4Ah) battery. My 1984 CB650SC starts immediately and all my lights are noticeably brighter.
I have never experienced a cold start problem. During the winter here in Oregon we had some 20 degree days and I was still riding my motorcycle no problem. Rode to College and it start right up no problem after sitting in the cold for hours.
I have no experience with the store bought batteries but I much prefer making them myself. A lot more fun.
