Does not topping off my lithium batteries enough have potential consequences?

Welcome to another edition of Todd’s Two-Minute Tech Tip Tuesday, brought to you by the National RV Training Academy, the largest hands-on RV training academy in America!

In this week’s video, we’re addressing a fantastic question from one of our dedicated viewers,
StuPedasso. He has a robust battery setup and some concerns about maintaining it. Let’s dive into his question and explore the best practices for managing an RV battery bank, particularly with lithium batteries.

StuPedasso’s Battery Setup and Question

StuPedasso has a pretty big battery bank with 600 amp hours of lithium batteries and 800 watts of solar panels. He mentions that his demand slightly exceeds the output of his solar panels, so he occasionally runs a gas generator or plugs in to top off his batteries every four to six days.

Here’s his main question: Does not fully charging the lithium battery system regularly have any consequences, such as shortening its lifespan or reducing total output?

Understanding Lithium Batteries and Their Management

First off, it’s impressive that you can go four to six days on just 800 watts of solar power before needing to top off your batteries. Many RVers would love to have that level of efficiency!

But let’s get into the meat of your question. Does not fully charging a lithium battery system regularly have consequences? The answer is yes, but let’s break down why.

Battery Balancing and Why It Matters

Lithium batteries, especially those used in RV applications like lithium iron phosphate (LiFePO4), have multiple cells inside them. For a nominal 12-volt lithium battery, there are typically four cells. Think of these cells as four separate batteries within the battery. Over time and usage, these cells can become unbalanced.

When cells are unbalanced, one may discharge faster than the others. If you never fully charge your battery to 100%, the Battery Management System (BMS) doesn’t have the chance to balance these cells properly. Balancing is crucial because if one cell becomes significantly weaker than the others, the BMS will limit the total capacity of the battery to protect it from over-discharge, effectively reducing the usable capacity and lifespan of the battery.

Charging Cycles and Absorption Mode

To maintain a healthy lithium battery bank, it’s recommended to charge them to 100% at least once every seven days and allow them to stay in absorption mode for about three hours. Absorption mode is a phase in the charging process where the voltage is held steady (typically around 14.5 to 14.6 volts) while the current gradually decreases as the battery reaches full charge.

This phase is crucial because it balances the cells inside the battery. The rule of thumb is to spend about 30 minutes in absorption mode for every 100 amp hours of battery capacity. Since you have a 600 amp-hour battery bank, you should aim to stay in absorption mode for approximately three hours to ensure proper balancing.

The Impact of Not Fully Charging

If you don’t regularly charge your batteries fully, they won’t be balanced properly. While this won’t cause immediate harm, over time, it will reduce the overall lifespan and capacity of your batteries. For example, if your battery has a 10-year warranty but you never fully charge it, you might only get six or seven years of life out of it. Additionally, if your battery manufacturer can determine through the BMS logs that the batteries were never fully charged, it could void your warranty.

Exceptions and Special Cases

Some batteries, like the Big Beard batteries mentioned in the video, have internal active balancing at a lower voltage. This means that they don’t require the higher voltage of the absorption phase to balance the cells. However, for most standard lithium batteries, regular full charges and absorption mode are necessary.

Practical Tips for Battery Maintenance

Given your setup and usage pattern, here are some tips to ensure you get the most out of your lithium batteries:

1. Regularly Monitor Your Battery Levels: Make sure to monitor your battery levels regularly, especially when using solar power, to avoid deep discharges and ensure timely recharges.
2. Use Your Generator or Shore Power for Full Charges: Since your solar panels don’t always meet your demand, use your generator or shore power to fully charge your batteries and allow them to stay in absorption mode every week.
3. Check Your Charging Equipment: Make sure your solar controller and inverter/charger are properly set up to enter absorption mode as needed. If you’re unsure, consult the manual or contact a professional to ensure everything is configured correctly.
4. Don’t Overthink Occasional Low Charges: If you occasionally don’t fully charge your batteries, it’s not the end of the world. The key is to ensure that it doesn’t become a consistent pattern.

Conclusion

Thank you, StuPedasso, for your excellent question! Remember, properly maintaining your lithium battery bank by ensuring regular full charges and balancing is crucial for maximizing both performance and lifespan. With the right practices, you can enjoy reliable and efficient power from your RV’s battery system for many years to come.

If you have any more questions or want to learn more about RV maintenance, visit RVTechCourse.com and explore our courses designed to make you an RV expert.