STEP 2 : Find out the Amp hour (capacity) and balance the voltage of each cell.

New Cells -

We won't have much concern on the cells Amp hour (capacity) and voltage balance if building a battery pack using cells newly purchased from a manufacturer because most probably all the cells capacity and voltage are the same.

Use a voltmeter to check the voltage of each cell, if the cells voltage are not equal we can put them in parallel using the battery holder as in the video below. Let the cells sit for a couple or more hours in parallel and the voltage will be balanced or equalized :

Next, group the cells into the configuration required base on your project, in this case 5P10S as shown in the photo below :

Recycle Cells -

If we are building battery pack using recycle cells from different brands/ manufacturers we need to charge/discharge the cells in order to find out the Amp hour (capacity) of each cell and to balance the voltage of every single cell.

This can be done using a battery charge in the photo below.

Try to search "18650 battery capacity test" in Youtube and you will find some instruction videos on how to charge/discharge to find out the Amp hour of each cell.

Next, use repackr.com to group the cells in parallel so that each parallel group has the same Amp hour (capacity), as photo below, 5P10S in this case. Voltage of all parallel groups need to be equal before connecting the groups in series.