# 18650, 20700A & Other Batteries, Conversions, Configurations

## Conversions

### Convert mAh to Watt Hours

The formula is (mAh)*(V)/1000 = (Wh).

Example: 2200 (mAh) * 3.7 (V) = 8140 / 1000 = 8.14Wh

### Convert Watt Hours to mAh

The formula is (Wh)*1000/(V) = (mAh).

Example: 7.92 (Wh) * 1000 = 7920 / 3.6 (V) = 2200

## Series and Parallel Battery Configurations

### Series

• Voltage combines.
• The Positive side of the battery is

### Parallel

• Voltage stays the same.

## Examples

S indicates the amount of cells connected in series and P indicates the amount of cells connected in parallel.

### 6SP3

In this case, if we are talking 18650 batteries, 3 are connected together and the voltage stays at 4.2, while the capacity increases. S indicates that we have 6 of 3 parallel connections so we combine the voltage 3.6 6 times, giving us 22.2 volts.

## Scenario 1

We would like to create a 12v 18650 battery back. We have 84 spare cells. First we’ll need to find out how many cells required to reach 12 volts. You could do 12/4.2 to get 2.857… we obviously can’t split cells so we round up to the nearest number so that would give us 3 cells. 4.2*3=12.6 which is fine.

So now we know we need 3 in Series that’s S3, now to increase the capacities. We’ve got 84 cells and we need to divide them equally. We should also keep the series consistent so we can’t have 1 with an extra battery.

84/3=28, so now we’ve concluded our pack is 3S28P. That’s 28 cells in 3 groups, connected together to then give us 1 positive and 1 negative connections.

### How to know what kind of capacity we’ll have?

Each cell, for instance has a capacity mAh of 2000.