Don’t Keep Lithium Batteries Directly in Line With Your Lead Acid

As lithium ion technology is becoming more readily available our team has noticed an outpour of questions. These are in regards to interconnecting lead acid and lithium ion battery banks. As pioneers in this field, Battle Born Batteries is the go-to resource for lithium tech and battery safety.

Why Different Battery Chemistries Don’t Mix

For battery safety, we do not recommend combining different types of lithium batteries and lead-acid batteries. This is because the load characteristics and capabilities of these batteries are drastically different which can lead to safety issues. Due to this, do not directly combine these batteries in parallel or series.

Our team of experts at Battle Born Batteries does not recommend that you ever mix batteries’ chemistry, or battery types. Doing so can be detrimental to your system in a number of ways. You run the risk of irreparably damaging your electrical system an can create a variety of electrical hazards.

Mixing battery types and chemistries can  lead to a multitude of issues. Across assorted brands of lithium, we do not recommend ever mixing brands because of the BMS (Battery Management System). Our BMS protects the battery from several potentially damaging scenarios. This ensures battery safety, by verifying the user and battery are not put into precarious situations.

Some of these scenarios include:

  • High/Low voltage protection
  • Short Circuit Protection (One time only)
  • High/Low Temperature Protection
  • Cold Charging Protection
  • Automatic Cell balancing

Danger Zone Without a Battery Isolator

Even though both battery types are classified as a 12V battery, a lead-acid battery sits at a nominal voltage of 12.6V while on the other hand, our lithium batteries sit at a nominal voltage of 13.6V.  The voltage difference of the two batteries, combined with the internal BMS within the lithium and lack of BMS within the lead-acid can create a variety of concerns for the health of your batteries and safety of your system.

When batteries are not at the same voltage or discharge at mismatched rates, the power flows quickly between them. When this happens, this creates heating issues within your system arise which can damage your batteries and onboard components.

Both lithium batteries and lead-acid batteries are rechargeable energy storage batteries, but they have very different characteristics. Without proper components in line to separate the two, the batteries cannot be used in conjunction. Please note that these components must meet the technical requirements, including protective measures.

As a result of the previously mentioned differences, our team strongly suggests you do not tie your lithium battery bank directly to your lead-acid batteries.

When to Connect Your Battle Born Batteries and Lead Acid Batteries

When you are looking to interconnect your lithium-ion batteries with your lead acid batteries, the only method we recommend  is with a battery isolator or DC to DC charger in line between the two. The most common application of this set up is for alternator charging. As you may be familiar with, to be able to successfully charge your lithium battery house bank while driving you will have to connect it to your alternator and starting battery setup. Please keep in mind that Battle Born Batteries should not be used for cranking applications such as turning over the engine, and you will need to keep your lead acid starting battery in place.

To be able to charge your lithium house bank you will need to place a battery isolator or DC to DC charger in line between the starting battery and your house bank. These components will separate the two battery chemistries and allow for a proper charge to go to your lithium house bank.

Charging Parameters for Chargers and Battery Isolators

In addition to the voltage difference, lithium is also capable of charging and discharging much faster than lead acid. As a result of these differences, lithium has a very specific charging profile that must be met by your charger. You will want to confirm your current charger is able to fully and properly charge your lithium batteries. Chargers can vary from one to three stage charging profiles depending on the make and model. Most of the time you are able to reprogram your existing chargers to match our batteries’ charging profiles. Below are some of the common settings you may see and our suggested charging parameters for your Battle Born Batteries.

  • Bulk: 14.2-14.6V
  • Absorption: 14.2-14.6V
  • Absorption Time: 30 min per battery
  • Float: 13.4-13.8V
  • Equalization: Disable if possible or set to 14.4V
  • Charging Current: 50A per 100Ah of battery

Connecting Your Battle Born Batteries and Lead-Acid Bank with a Battery Isolator

To ensure battery safety, you need an isolating unit in line between your starting battery and your lithium house bank. You need this unit in line because lithium sits at a higher voltage and requires different charging parameters than lead acid. An isolating unit will disconnect the line between the batteries so that your lithium batteries do not continuously feed power into your starting battery. You can isolate your two battery banks with a battery isolator or a DC to DC charger depending on your system needs and preferences.

When choosing your isolating component, you will want to make sure that it is recommended by the Battle Born Battery team. Even if a component is deemed a battery isolator, it may not allow for a proper charge to your lithium bank. This often is the case when the isolator is strictly a voltage based unit.

Battle Born recommends the Victron Orion TR Smart 12/12V-30A Isolated DC to DC Charger for charging needs. This DC to DC charger is easily programmable for a proper lithium profile and is Bluetooth compatible as well.

For a Battery Isolator our team recommends using the LI-BIM. This unit is preprogrammed with the correct lithium charging profile. It also duty cycles your alternator periodically and will monitor your starting battery and lithium house bank to prioritize the charge. Below is a layout of the connections you need to make with the LI-BIM to properly isolate your two battery banks.Isolating Lithium and Lead Acid Battery Bank with Battery Isolator


If you have any additional questions about your battery bank check out our FAQ, give our sales and tech team a call at (855) 292-2831 or send an email to [email protected].

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