We’re often asked if it’s possible to use a lead-acid starting battery alongside LiFePO4 house batteries, charging both from the same alternator. The answer is generally yes, but it requires some special considerations. Lead-acid (or AGM) and LiFePO4 batteries are different technologies with incompatible charging requirements, so they should never be combined directly. This means a battery combiner is not suitable. However, there are two viable options for charging both battery banks from a single alternator.
One effective solution is using a DC-DC charger, which allows the alternator to charge both battery types while keeping them electrically isolated. The Victron Orion DC-DC charger is an excellent choice for this purpose. It enables the starting battery to charge directly from the alternator, while providing a separate charging profile suited to the LiFePO4 house batteries. The benefits of this setup include:
- Independent charging for different battery types
- Multiple charging profiles tailored to each battery type
- Straightforward installation and monitoring
- Alternator protection
- Expandable: multiple Orion units can be connected in parallel for higher power charging
The Orion is available in both isolated and non-isolated models. The isolated version is suitable for applications where the battery banks do not share a common ground, such as some vehicle and marine setups. The non-isolated version is designed for systems with a common ground, which is typical in most marine installations, making it the appropriate choice for many boats.
Below is a wiring diagram for a single Orion DC-DC charger with two battery banks:
A battery isolator enables the charging of multiple battery banks while keeping them isolated from each other. The Victron ARGO FET Battery Isolator enables the charging of three battery banks. The disadvantage of this approach is that there is a single charging profile applied to all three battery banks. Thus, if the start battery has a significantly different charging profile from the LiFePO4 battery bank, this may not be a good option.
Advantage – multiple batteries can be charged independently.
Disadvantage – only one battery charging profile.
Additions to this article:
Advanced Solution for Mixed Battery Systems: Battery-to-Battery (B2B) Chargers
While the above methods offer solutions for charging different battery types, the most advanced and effective approach, particularly when combining a lead-acid start battery with a LiFePO4 house bank, is using a Battery-to-Battery (B2B) charger, also known as a DC-DC charger. These intelligent devices have become the gold standard for modern dual battery systems.
How B2B Chargers Work:
A B2B charger takes power from your alternator (or another DC source like a generator) and converts it to a precise, multi-stage charging profile tailored for your LiFePO4 house battery. It acts as a smart intermediary between your starting battery and your house bank, ensuring each receives the optimal charge.
- Isolated Charging: B2B chargers isolate the charging circuits of the two battery types, preventing them from interfering with each other.
- Optimized Charging Profile: They deliver a controlled, multi-stage charging profile (bulk, absorption, float) that is optimal for LiFePO4 batteries, maximizing their lifespan and performance. This differs significantly from the charging profile required for lead-acid batteries.
- Voltage Regulation: B2B chargers carefully regulate the voltage and current delivered to the house battery, preventing overcharging and damage.
- Current Limiting: Many B2B chargers allow you to limit the charging current, protecting both your alternator and your batteries.
- Temperature Compensation: Some advanced B2B chargers feature temperature compensation to adjust the charging profile based on ambient conditions, further optimizing performance.
- Ignition Sense: They will typically have an ignition sense wire, so they know when the engine is running. They often also have a voltage sense feature built in, so they know when the starter battery is being charged.
Benefits of Using a B2B Charger:
- Protects Your Batteries: Ensures that both your starting and house batteries are charged safely and effectively, preventing damage and maximizing their lifespan.
- Maximizes LiFePO4 Performance: Provides the ideal charging profile for LiFePO4 batteries, ensuring they reach their full potential and deliver optimal performance.
- Protects Your Alternator: Prevents your alternator from being overloaded by managing the charging current.
- Simplified Installation: While slightly more complex than a VSR, modern B2B chargers are generally straightforward to install.
- Peace of Mind: Offers a reliable and worry-free solution for charging your dual battery system.
Choosing the Right B2B Charger:
When selecting a B2B charger, consider the following:
- Charging Current: Choose a charger with a charging current appropriate for your LiFePO4 battery bank's capacity and your alternator's output.
- Battery Chemistry Compatibility: Ensure the charger supports both lead-acid and LiFePO4 battery chemistries.
- Features: Look for features like temperature compensation, remote monitoring, and adjustable charging parameters, if needed.
- Brand Reputation: Opt for a reputable brand known for quality and reliability. Some of the top names include Redarc, Victron, Renogy, and Sterling.
- Install: B2B chargers are relatively easy to install. Run positive and negative cables between your starter battery and B2B charger, then do the same between the B2B charger and your house batteries. Run an ignition wire from a circuit that is live when the engine is on, to the ignition sense terminal on the charger.
Conclusion to the B2B Charger Section:
In conclusion, Battery-to-Battery chargers offer a superior solution for managing a dual battery system with different battery chemistries. They provide a level of protection, efficiency, and performance that VSRs and other simpler methods cannot match, particularly when dealing with the advanced charging needs of LiFePO4 batteries. By investing in a quality B2B charger, you are investing in the long-term health and performance of your batteries and the overall reliability of your electrical system.