How to Increase the Capacity of Lithium Batteries ? What Are the Differences Between Series and Parallel Connections of Lithium Batteries?

The feature of parallel lithium batteries: voltage remains constant, battery capacities add up, internal resistance decreases, and power supply duration is extended. According to parallel theory, the main current equals the sum of the branch currents; Thus, to achieve the same charging efficiency as a single cell, the charging current for n parallel lithium batteries should be the sum of the currents of n batteries, which is reasonable under Ohm's Law: I=U/R. However, the internal resistance of parallel batteries will change; According to the parallel resistance formula, the total internal resistance of two parallel lithium batteries equals the product of their resistances divided by the sum of their resistances, decreasing as the number of parallel batteries increases.

When connecting lithium batteries in parallel, it is crucial to ensure consistency of lithium batteries . Poorly matched parallel batteries can cause charging issues or overcharging, damaging the battery structure and affecting the lifespan of the entire battery group. Thus, when selecting parallel batteries, it’s advisable to avoid mixing different brands and capacity. The internal requirements for battery consistency : voltage difference ≤ 10mV, internal resistance difference ≤ 5mΩ, and capacity difference ≤ 20mA.

After connecting lithium batteries in series, the voltages add up and the currents are equal, thereby increasing voltage. For example , if two piece of 3.7v 2200mah lithium ion battery in series , the total voltage is 7.4v 2200mah lithium battery .In parallel connections, the voltage remains constant (Sure that the voltages of the batteries are the same; otherwise, a higher voltage will charge the lower voltage, which can be dangerous if the difference is too huge), thereby increasing capacity .

Differences Between Series and Parallel Connections:

Series Connection:

This means connecting the batteries end to end, where the positive terminal of the first battery connects to the negative terminal of the second battery, and so forth. The total voltage is the sum of the each battery voltages, while the current through each battery remains equal. If one cell of entire battery pack is damage which will cause the entire battery group unusable or reduce the voltage; series connections can increase the total voltage.

Parallel Connection:

This means connecting all positive terminals together and all negative terminals together. The total voltage is equal to that of a single battery, while the current is the sum of all battery currents. Although the battery group's lifespan is enhanced, damage  caused by short-circuit currents can be more severe; parallel connections increase the total current.

Whether in series or parallel connection , the output power of the battery group will be increased.

www.liliangbattery.com 

Carry Zhang