Soldering direct applies to much heat to the cells usually 3 - 4 seconds of heat is to much, spot welding takes milliseconds and is instant with little heat to internally damage the cells. Excessive heat and prolonged heat damages cells causing internal resistance and capacity loss in the log run.
Paralleling (P) x number of cells together determines the batter capacity in Ah and amps discharge rating.
2900Mah 10A cells x 4 in P = 11.6ah @ 40a discharge rating, 5P = 14.5ah @ 50a discharge and so forth.
To get a parallel string/row / you tab all the pos ends together and all the neg ends together, do this 10 times for a 36v battery. Then you have to connect the P strings in series (S).
For a 24v battery we need 7 of these P strings connected in Series (S) to give us 29.4v max charge. 36v needs x 10 of these P strings for 42v max charge and 48v needs x 12 of these P strings for 50.4v max charge.
To connect in series is the dangerous bit get it wrong and BANG KAPOW holly smoke Batman.
Each string/row is tabbed together so the ions flow from one end to the other smoothly, pos to neg , pos to neg all the way through. For a 10S 36v battery we have 10 strings already tabbed in P, to tab them together in series the first String is placed neg up, 2nd pos down, 3rd neg up and so forth. Each P string is connected to the next P string alternately so first string pos is tabbed to 2nd string neg, 2nd string pos tabbed to 3rd string neg then 3rd string pos to 4th string neg and so forth.
When looking at a side view of a battery you should be able to trace the connecting tabs to form an up and down continuous connecting flow from one end to the other.
