Why would I use an External Alternator Regulator to charge my batteries?

Should you use an external alternator regulator to charge your deep-cycle lithium or lead acid batteries?

Wanting to know what else you will need to optimize your energy system? Will this additional investment easily fit into your energy system?

You are interested in investing in upgrading the energy system in your RV, Van or Boat. One of the first things you need to know is if you should use an external alternator regulator to charge your batteries. Protecting your new investment from both short-term and long-term damage is the primary function that ARCO had in mind when building Zeus, the high energy alternator regulator.

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Here are reasons why you should use an external alternator regulator to charge your batteries:

Temperature compensation during charging:

Deep-cycle lead-acid batteries are used in a variety of applications, including solar panels, RVs, and power tools. They are designed to be discharged and recharged hundreds of times, making them a good choice for applications where a constant power supply is needed.

Like any battery, deep-cycle lead-acid batteries are sensitive to temperature. As the temperature of the battery increases, the chemical reactions that take place during charging and discharging speed up. This can lead to the battery overheating and being damaged.

To prevent this, manufacturers of deep-cycle lead-acid batteries require temperature compensated charging. This means battery voltage is adjusted up or down based on actual battery temperature. In other words, a battery that charges at 14.4V at 77F cannot charge at 14.4V at 90F. Internal voltage regulators that come in most modern alternators have no way to temperature compensate for the batteries’ physical temperature.  This is because they are designed to maintain a constant voltage, regardless of the temperature. As a result, if a battery is charged at a constant voltage in hot weather, it can overheat and be damaged.

For this reason, it is important to use an external alternator regulator that accounts for temperature when charging deep-cycle lead-acid batteries. This will help to ensure that the battery is charged properly and does not overheat.

LiFePo4 batteries have very strict charging voltages and maximum absorption duration:

This is because LiFePo4 batteries are more sensitive to overcharging and overcurrent than other types of batteries. If a LiFePo4 battery is overcharged, it can overheat and damage the battery. The maximum absorption duration is the amount of time that a LiFePo4 battery can be charged at a constant voltage. If the absorption duration is too long, the battery can overheat and damage the cells.

A stock internal regulator cannot be programmed for LiFePO4, nor can the absorption duration be modified. If a stock internal regulator is used to charge a LiFePo4 battery, it can overcharge the battery, or the battery will pull too much amperage from the alternator and burn the alternator out.

To properly charge a LiFePo4 battery, it is important to use an external alternator regulator that recognizes the LiFePo4 battery chemistry that it is charging. These alternator regulators have built-in safety features that prevent overcharging and overcurrent, and some have pre-set and customizable battery chemistry settings. They also have adjustable charging voltages and absorption durations, which allows you to customize the charging process for your specific battery.

Stock internal alternator regulators are designed for starter batteries.

Internally regulated alternators are designed to charge a starting battery, not a massive house battery bank. When used to charge a large house battery bank, an internally regulated alternator can be overworked and overheated, leading to premature failure. This is because internally regulated alternators use a fixed voltage setting, which means that they cannot adjust their output to match the needs of the battery bank. As a result, the alternator may be forced to work harder than it is designed to, which can lead to heat damage.

External alternator regulators offer a number of advantages over internally regulated alternators, including:

  • Better heat management: External alternator regulators have a temperature sensor that monitors the actual alternator temperature and adjusts the alternator's current output to keep the alternator to a safe working temperature. This helps to prevent premature failure of the alternator.
  • More precise charging: External alternator regulators can provide a more precise charging profile to the battery bank, which can help to extend the battery life.
  • Flexibility: External alternator regulators can be used with a wider range of alternators than internally regulated alternators. This makes them a good option for vehicles with older or high-output alternators.

If you have a large house battery bank, it is important to use an external alternator regulator to protect your alternator and extend the life of your batteries. External alternator regulators are a relatively inexpensive investment that can save you money in the long run.

Internal alternator regulators only have two stages of charging.

Internally alternator regulators have two stages of charging: Bulk and Absorption. The Bulk stage is where the alternator puts out the most current to quickly charge the battery. Once the battery voltage reaches a certain level, the alternator switches to the Absorption stage, where it reduces the current output and holds the battery voltage at a slightly higher level. This allows the battery to absorb the full charge.

In the Float stage for batteries such as LifePo4 and lead acid, the alternator maintains the battery voltage at a lower level, typically around 13.2-13.8 volts for lead acid batteries and around 13.3-13.4 volts for LiFePo4 batteries. This prevents the battery from overcharging and damaging the cells.

Internally regulated alternators do not have a Float stage. Once the battery reaches the Absorption voltage, the alternator will continue to hold that voltage indefinitely. This can lead to overcharging for deep-cycle batteries, especially LiFePo4 batteries. Overcharging can damage the battery cells and shorten the battery's lifespan.

For this reason, it is not recommended to use an internally regulated alternator to charge deep-cycle batteries. If you have a deep-cycle battery in your RV or boat should consider installing an external battery Alternator regulator with a three-stage charging process. This will help to ensure that your battery is properly charged and protected from damage.

External smart alternator regulators offer multiple charging stages that can be programmed to exactly match the manufacturers charging requirements.

charging batteries for sailboat, rv, and van


In this article we hope that you have a clearer picture when deciding if adding an alternator regulator to your system will fit your current and future needs.

An external alternator regulator is a device that controls the voltage and current output of an alternator. It is used to protect batteries from overcharging and undercharging, and to extend their lifespan.

There are several reasons why you should use an external alternator regulator to charge your batteries, including:

  • Temperature compensation: External alternator regulators can compensate for the temperature of the battery, which is important for deep-cycle lead-acid batteries and LiFePo4 batteries. This helps to prevent the batteries from overheating and being damaged.
  • Multiple charging stages: External alternator regulators can provide multiple charging stages, such as bulk, absorption, and float. This helps to ensure that the batteries are fully charged without being overcharged.
  • Overcharging protection: External alternator regulators have built-in overcharging protection, which helps to prevent the batteries from being damaged.

If you have deep-cycle batteries in your RV, van, or boat, you should consider using an external alternator regulator to protect them and extend their lifespan.

Here are some additional benefits of using an external alternator regulator:

  • Improved battery performance: External alternator regulators can help to improve the performance of your batteries by providing them with a more consistent charging profile. This can lead to longer battery life and better performance underload.
  • Reduced maintenance: External alternator regulators can help to reduce the amount of maintenance required for your batteries. This is because they can prevent the batteries from being overcharged or undercharged, which can lead to premature failure.
  • Peace of mind: External alternator regulators can give you peace of mind knowing that your batteries are being properly charged and protected. This is especially important if you rely on your batteries for power in your RV, van, or boat.

If you are considering upgrading the energy system in your RV, van, or boat, we recommend that you talk to a qualified electrician about installing an external alternator regulator. This is a relatively inexpensive investment that can save you money in the long run by extending the lifespan of your batteries and improving their performance.

If you plan to speak with a professional about installing an external alternator regulator, we recommend you learn more about this addition in our learning center.