Can a lithium ion battery pack have multiple strings?

Whenever possible, using a single string of lithium cells is usually the preferred configuration for a lithium ion battery pack as it is the lowest cost and simplest. However, sometimes it may be necessary to use multiple strings of cells. Here are a few reasons that parallel strings may be necessary:

Why do we connect multiple lithium batteries to a string of batteries?

Connecting multiple lithium batteries into a string of batteries allows us to build a battery bank with the potential to operate at an increased voltage, or with increased capacity and runtime, or both.

What if there are only two batteries in a parallel string?

If there are only two batteries in the parallel string, we would then take a cable from the POS. (+) terminal of Battery 1 to the charger. We would use the POS. (+) terminal of Battery 2 for connection to the loads.

What if there are only two batteries in a series string?

If there are only two batteries in the series string (Figure 1), we would then take a cable from the open POS. (+) terminal of the first battery and a cable from the open NEG. (-) of the second (last) battery in the string to the load and charger/power source.

How many volts are in a battery pack?

If each cell is 10 amp hours and 3.3 volts, the battery pack above would be 10 amp hours and 26.4 volts (3.3 volts x 8 cells). For this setup, a BMS capable of monitoring 8 cells in series is necessary. Lithium cells can almost always be paralleled directly together to essentially create a larger cell.

Should a battery charger be connected to a parallel string?

Installers should always avoid connecting loads and charging/power sources to the same battery in a parallel string. Properly ensuring that loads and charging source connections are made to apposing ends of the string will ensure the bank stays in a more balanced state and can prevent premature battery failure.