Is It Dangerous to Mix Battery Sizes?

When you’re building a battery bank for your off-grid application, it can be tempting to mix and match different battery sizes. Simply put, the answer is NO.

For the longer explanation on why this is a very bad idea, keep reading.

Mixing Battery Sizes: What Happens?

You cannot connect batteries of different amp-hours in series with good results.

We strongly recommend you DO NOT attempt to mix battery sizes (amp-hours) and connect together. Due to differences in battery management systems and battery cell counts, there may be a charging and voltage discrepancy between batteries.

This will cause the highest voltage battery to charge the lowest voltage battery attempting to create balance in the circuit. The greater the difference in voltage, the higher the probability of battery failure.

Can I Connect 100 Amp-Hour Batteries to the 300 Amp-Hour Batteries?

These two different sizes of batteries should never be connected. Any attempt to connect batteries of different amp-hours will result in a voided warranty.

You should only ever connect batteries of the same size.

How Do I Connect Same Sized Batteries?

You may use two different types of connections for batteries of the same voltage and amp-hours together to make a larger bank.

Proper Battery Connections

Parallel Connections – These connections are used when you want to increase the amperage of your battery bank. Most commonly, parallel-only connections are found in 12V systems.

The connections on this type of battery bank go from positive to positive and negative to negative.  Connecting this way will double your amps (see diagram below).

Series Connections – This type of connection is used when you need to increase the voltage of your battery bank. These types of battery connections are found in all types of battery banks including 12V, 24V, and 48V systems. 

For instance, making a connection to the positive and negative terminals in this orientation is different than a parallel connection. Doing so links the batteries together increases the voltage of the battery bank (see diagram below).

Mixing Connections Vs. Mixing Battery Sizes

In some instances with a larger size battery bank, it is common to have series and parallel connections in your battery bank.

However, you should never be connecting different battery sizes together in the same bank!

Let us know if you have any additional questions about LiFePO4 batteries . Also, join us on Facebook, Twitter, LinkedIn and YouTube to learn more about how lithium battery systems can power your lifestyle!