When you're building a battery bank for your mobile or 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 Battle Born Batteries to the 270 Amp-Hour Battle Born Batteries?
Here at Battle Born Batteries, we offer two different lithium battery sizes: our 100 Amp-Hour BB100 series and GC2 series, and the new 270 Amp-hour batteries.
These two different sizes of batteries should never be connected. Any attempt to connect Battle Born 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).
*If you plan to wire your batteries in series, please let us know when you place your order so we can make sure to match your capacity.
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!
The Importance of a Reliable battery Management System
In line with the proper battery size for your system, a Battery Management System is another component of a well-managed and maintained lithium battery system. Lets take a look at what that looks like.
A battery management system (BMS) is an electronic system that manages rechargeable batteries, including individual cells or battery packs. It ensures the battery operates within a safe area by monitoring its state, calculating secondary data, reporting it, controlling its environment, authenticating it, and balancing it.
How Does a Battery Management System (BMS) Work?
The individual cells within a battery pack are monitored by the battery management system to ensure safe operation. By calculating the current capacity of each cell, the BMS regulates the charging and discharging to void damaging the battery. Through current limits, the BMS prevents the battery from being overcharged or overdrawing the source and load. This protection ensures that cell voltages remain within a safe range, enhancing the battery's longevity.
The BMS also keeps track of the battery's remaining charge by monitoring the energy flow and cell voltages in and out of the battery pack. When the battery is depleted, the BMS automatically shuts it down. Unlike lead-acid batteries, lithium-ion batteries do not exhibit signs of degradation but simply turn off when the charge runs out.
Built-In Safety Features
At Battle Born Batteries, our proprietary internal BMS system has three different levels.
- The first level is 100 amps continuous, or 1200 watts at 12 volts. This means the battery can provide a continuous current of 100 amps until the battery is fully depleted.
- The second level is 200 amps for 30 seconds (2400 watts at 12 volts). This level allows the batter to handle device surges of up to 2400 watts for a period of 30 seconds.
- The third level is a ½ second surge up to the battery's maximum capacity. If a high moment over 200 amps happens, the battery can handle it for ½ second.
Our battery management system has a safety feature that continuously limits the current to 100 amps and will cut off any surge over 200 amps after half a second.
BMS and High Current Disconnects
If a current in the system exceeds a certain threshold, a Battle Born Battery will disconnect and attempt to reconnect after five seconds, vis the BMS. This safety feature protects the battery and informs the user that it is approaching its designed threshold. This is a huge benefit for batteries stored in hard-to-reach places, such as RVs and marine applications. In alignment with this, a BMS system is a requirement for marine applications according to new ABYC standards that have been ratified.
Let us know if you have any additional questions about wiring or want to purchase more batteries for your system. Check out our website or give our sales and tech team a call at 855-292-2831.
