Skip to content
An Unbound Renewable Energy Company
Open Mon-Fri: 6am to 5pm PST

How Do I Maintain Deep-Cycle Batteries?

  • Program your voltage set points so that the battery bank charges at the proper voltage.
  • Refill flooded lead-acid batteries with distilled water every 2-4 weeks as needed.
  • Regularly check battery state of charge. Apply an equalization charge to flooded batteries every 90 days. (Do not equalize sealed lead-acid or lithium batteries.)
  • Clean terminal connections and cables to prevent corrosion.

Solar batteries are the most costly component of any off-grid solar system. It’s important to program them properly and stick to a regular battery maintenance schedule to keep them running efficiently for years. Neglecting the proper setup and maintenance routine can shorten the lifespan of your batteries and void the product warranty.

Some battery types, like Lithium-ion, require little to no maintenance after the initial setup. Other battery types (especially flooded lead-acid) need regular upkeep to stay in good condition.

No matter what type of batteries you own, this article will help you program your battery bank and give some battery maintenance tips to keep your system running smoothly.

FREE Solar Battery Guide

Initial Programming

The first time you bring your system online, you’ll need to program your battery chargers to the proper charging settings for your battery bank. These settings dictate parameters like charging voltage and current.

This is where you program voltage set points, the charging voltages applied to the battery during each stage of the charging cycle. Batteries typically charge in 3 phases—bulk, absorb, and float, which can be summarized as follows:

  • Bulk: High current to replenish charge and bring voltage up as quickly as possible (below 80%)
  • Absorb: Charge rate slows as batteries approach full state of charge (~80-100%)
  • Float: Batteries receive a trickle charge at 100% to stay fully charged

Each stage requires the charger to be set at a specific voltage, which is based on the requirements of your battery.

Programming the voltage set points accurately is critical to ensuring the long-term health of your batteries. Setting the wrong charge parameters will make your batteries charge improperly, shortening their lifespan.

There are other values to set during the initial programming phase as well:

  • Absorb time: The amount of time the charger spends in the absorb phase.
  • AC input amps: Maximum input current from grid or generator, to ensure the combined current from the battery charger and loads doesn’t exceed the rating of the generator. Depends on generator size or grid input breaker. See manual for details.
  • Max charge rate or charge current limit: Maximum charging current, either expressed as a percentage of the charger output or total maximum charging amps. This setting is used to limit charger output, to make sure your batteries are not overcharged with too much current.
  • Temperature compensation: Adjusts the battery charger for operation in various temperature ranges. Most chargers include a battery temperature sensor.

These settings are different for every battery and charger. Check the spec sheets or installation manuals for your batteries and chargers to find the specific values for each of the above settings.

Programming your equipment according to the settings recommended in the manual is the first step toward ensuring the long-term health of your battery bank.

Flooded Lead-Acid Battery Maintenance Tips

Flooded lead-acid batteries require regular maintenance to function properly. We recommend checks every 2-4 weeks to keep the battery bank tuned up.

Note: always follow proper safety procedures when working around batteries. Wear eye protection and gloves, remove any jewelry, and secure loose clothing and long hair.

Add distilled water every 2-4 weeks

Flooded lead-acid batteries lose water during the charge cycle. They must be refilled regularly with distilled water to function properly and stay healthy.

Note that you should only use distilled water. Non-distilled water (like tap water) will introduce small particles and contaminants, which weakens the battery chemistry.

Adding distilled water every 2-4 weeks is key to maintaining your flooded batteries.

Check water levels every 15-30 days and refill as necessary. Your watering schedule depends on your local climate, charge settings and specific application. It may be useful to keep a log to track how often your batteries need to be refilled.

  1. Check water level when batteries are fully charged.
  2. Open the vent well to check the water level.
  3. Add water to just below the maximum water level line. DO NOT overfill past this line. The battery installation manual should indicate where to find the maximum water level line.

Check battery state of charge (SoC):

Use a refractometer to keep an eye on how charged your batteries are. The refractometer measures the specific gravity of your batteries. This video explains how to use a refractometer:

Consult the charts published by your battery manufacturer to find your battery state of charge based on their specific gravity reading. An example chart is shown below.

If your batteries are not holding charge even after a full charge cycle and equalization, they are likely defective, damaged, or have reached the end of their lifespan and are starting to lose some capacity.

Some inverters use a battery monitor to measure state of charge. These battery monitors typically rely on a shunt for measuring the total current coming in and out of the battery bank.

Battery monitors are a useful tool for daily monitoring, but they require proper setup. If they aren’t installed or programmed correctly they can provide false readings.

Even if you have a battery monitor, we still recommend checking the specific gravity with a refractometer on a regular basis. It helps verify the battery monitor is accurate and ensures your batteries reach a full charge.

Refractometers measure the specific gravity of your batteries.

Equalization Charges

Batteries should be equalized occasionally to make sure each cell is equally charged. Apply a controlled overcharge once every 30-90 days, or whenever individual batteries are imbalanced (reading a different voltage or specific gravity).

  1. Check water level before initiating an equalize charge.
  2. Turn off any loads.
  3. Set your charger at the Equalize voltage specified in your battery manual.
  4. Start the Equalize charge. Gassing and bubbling is normal during this process.
  5. Stop charging and take specific gravity readings every hour. The EQ process is complete when the specific gravity stops rising.

Other Routine Flooded Lead-Acid Battery Maintenance

  • Tighten the battery cable connections as needed. Wear gloves/eye protection and use insulated tools.
  • Clean terminal connections & cables to prevent corrosion. Mix baking soda and distilled water into a paste and apply with a wire brush. Rinse cleaning residue and dry with a cloth or paper towel.
  • Keep the top of the batteries clean from dust and debris to avoid creating a current pathway or electrical leakage across the top of the battery.

Sealed Lead-Acid Battery Maintenance

Sealed lead-acid batteries do not need to be filled with water or equalized. They require very little maintenance other than the occasional check-up on the battery’s state of charge.

Check Battery State of Charge (SoC):

Use a multimeter to keep an eye on how charged your sealed lead-acid batteries are based on the voltage. A multimeter is equipped with positive and negative probes which allows the meter to get a DC voltage reading from the battery.

Multimeters give a DC voltage reading from your batteries.

Your battery manual should contain a chart that estimates the battery’s state of charge based on these voltage readings (like the one in the previous section).

To get the most accurate reading, your batteries should be tested in a resting state. Let your batteries rest for at least 2 hours (no charging/discharging) before taking the voltage reading. Attempting to use the multimeter when batteries are being charged or discharged is going to result in a higher or lower voltage, depending on the load.

If your batteries fail to approach 100% SoC even after a full charge cycle, they are likely defective, damaged, or have reached the end of their lifespan.

Equalization Charges

DO NOT equalize sealed batteries! This applies to flooded lead-acid batteries only.

Other Maintenance

  • Tighten the battery cable connections as needed. Wear gloves/eye protection and use insulated tools.
  • Keep the top of the batteries clean to prevent them from getting dusty and grimy.

Lithium-Ion Battery Maintenance

Fortunately, lithium batteries require little to no maintenance (one of the main appeals when comparing lithium vs. lead-acid batteries). Once they are set up properly, they don’t need any checks aside from the occasional state-of-charge reading to ensure they are holding a charge.

Lithium battery manufacturers sell a tool to gauge the battery’s state of charge (SoC). The tool typically communicates with the built-in Battery Management System (BMS) to get an accurate SoC reading. Simply hook the monitoring tool up to the battery and read the SoC value from the display screen.

Discover Battery makes their own monitoring tool called a Battery Discharge Indicator.

Other Maintenance

  • Tighten the battery cable connections as needed. Wear gloves/eye protection and use insulated tools.
  • Keep the top of the batteries clean to prevent them from getting dusty and grimy.

A Note About System Design

That’s it for our maintenance tips, but it’s worth pointing out that maintenance is only effective if your system is well-designed and your battery bank has been properly sized.

In our experience, many cases of battery bank failure can be attributed to poor system design. People buy the wrong size battery bank or solar array, not taking into account key factors like temperature, local sun hours, and discharge depth. If you simply don’t have enough panels to fully charge your batteries, they’re destined to fail at some point.

The solar array, battery bank and inverter all need to be the proper sizes for the batteries to stay healthy. You also need enough amperage left over to charge the battery bank after accounting for loads that need to be powered (15 charging amps per 100ah is recommended for lead acid batteries). Take a look at our off-grid system sizing guide for more info.

Stuck on system design? Get in touch for a free consultation with one of our solar designers. We provide design advice that is tailored to your application, and our in-house tech team closely reviews proposed plans to avoid the common pitfalls outlined above.

More Battery Maintenance Resources

If you follow this guide, you’re well on your way to ensuring a long lifespan and peak performance from your battery bank. For more battery advice, grab our free Solar Battery Guide linked below.

New call-to-action

Related Articles

SolarEdge HD-Wave Review: Pros & Cons, Pricing, Specs (2021 Edition)

The SolarEdge HD-Wave is our most popular inverter. While it’s…
Read More >

What Does a Solar Ready Mandate Mean for Builders?

As a builder, you've been following the latest home trends.…
Read More >

Leave Rising Utility Costs Behind: Learn How to Harness Energy Independence

Energy keeps our homes running smoothly.  Without it, we'd struggle…
Read More >