The night before, I’d taken the airplane out of its storage state, hoping I hadn’t forgotten anything. “I need to move to a warmer climate so I can fly every day,” I thought. I couldn’t wait to get in the air. A friend and I had decided to meet for lunch at a location 30 minutes away.

I entered the aircraft and went through the checklist. Good. Master on. I turned the key.

Nothing. Absolutely nothing.

“How can this be?” I said to myself. Then the realization hit me that I had totally forgotten about the battery. I had not taken it out of the airplane for testing or charging. I felt a crush of disappointment as I pulled my phone out to call my friend.

 * * *

An assortment of calamities can ground a flight unexpectedly. A dead battery is one of them. We all have a story about a dead battery, and they are not happy stories. Some of these stories end up with runaway aircraft after a hand propping goes wrong.

The good news is that battery technology has come a long way in the last decade. Since I last wrote about battery choices nearly four years ago, we’ve seen lots of improvements. With a small amount of attention and good equipment choices, it is rare now to find yourself stuck somewhere. Here’s what you should know to keep this particular surprise away.

As wonderful as advancing technology is, it presents a confusing array of products. From headphones to navigation electronics, it feels as if we have to spend days reading the reviews before we can purchase anything. Even mundane items in the grocery store present choice challenges. Just picking out a carton of eggs in a case with 30 different brands is no easy task.

The Tech

Even though it feels like the advancements can be slow for electronics in aircraft, just look at the last 20 years. Now glass panels in newer cockpits are commonplace. But we might feel like it snuck up on us.

Lead-Acid Batteries

These are considered “old” tech but are still being used reliably in more than 70 percent of small aircraft. This is because they are (relatively) inexpensive and can last three to five years if cared for.

The sealed versions — most commonly known as absorbent glass mat, or AGM — are a substantial improvement over the “flooded” or “wet” lead-acid batteries many of us are used to.

If you’re still using the flooded cell version, I recommend you move to a sealed lead acid (SLA) version on your next purchase. You’ll have much less maintenance and fewer worries around leaks and the associated corrosion. If you fly aerobatics, then you’ve been using SLA batteries all along.

Lithium

Twice this month I have seen newspaper stories about consumer lithium batteries catching fire on commercial aircraft (passenger cabin) and in electric bicycle shops. You may be thinking that we should have solved the problem by now. Why would you want to use lithium-ion tech to start your airplane if they continue to have this many problems?

But there’s a common theme running through the stories. Nearly all the incidents that have captured the headlines are either related to nonapproved manufacturers of lithium batteries (containing defects), not following charging instructions (leaving a battery on charge in a confined or hot area for too long), or using the wrong or incorrectly manufactured charger.

A correctly matched, correctly manufactured, correctly charged lithium aircraft battery is safe. The latest tech around lithium batteries for aircraft is in the form of LiFePO₄ or LFP (lithium iron phosphate). These chemistries don’t have the tendency to overheat as much as lithium-ion.

Future tech includes sodium-ion or solid-state batteries, also safer in terms of thermal runaway events. LFP batteries are up to 80 percent lighter than lead-acid versions. This is great news as we keep adding things to our airplanes every year and wonder why they get heavier and heavier.

If you fly a certified aircraft, lithium battery supplemental type certificates (STCs) are available for many models, and they may be bundled with the battery cost-wise. For a Cessna 182, for example, you’ll pay less than twice as much for an EarthX LiFePO₄ (LFP) over a sealed lead-acid battery, and the price includes the STC.

More choices are available for homebuilt aircraft — EarthX is the most well-known. The prices for EarthX batteries for experimentals are reasonable and are not a lot more than the price of a good sealed lead-acid battery.

LFP batteries come with a battery management system (BMS) that balances cell voltages, preventing under- and over-voltage conditions, and fail-safe triggers that will disconnect the battery if it senses a thermal runaway or short-circuit condition. These systems have a simple panel light and/or an interface for other digital electronics in your panel.

An in-depth review of specific battery manufacturers can be found in the March 2023 issue of The Aviation Consumer, Belvoir Media (now Flying Media Group), and in the June 2023 issue of KITPLANES, Belvoir Media. These issues are available online to subscribers.

Taking Care of What You Have

Doing the following can help extend the life of your wet lead-acid or sealed lead-acid battery:

• At a temperature of 80 degrees Fahrenheit, a lead-acid battery will self-discharge at a rate of 4 percent a week. These batteries are at their best and last longest when they are at full charge. Keep your battery on a battery maintainer (tender) that is designed for your specific battery. I don’t recommend using an automotive battery charger or trickle charger with aircraft batteries. Automotive chargers are often set at a higher output voltage, do not compensate for temperature, and use high amperage for fast charging. This boils down to understanding that batteries built for cars and trucks are a different animal than the ones built for aircraft, even though they may output a similar 12 volts.
• If you are going to be testing or setting up electronics, or just sitting in your airplane playing (you don’t do this?), don’t use airplane power; use an external power unit. This will be the same box you used to install and test all your electronics when you built the airplane. This practice will save wear and tear on your battery, and it will last longer.
• Buy or borrow a good capacity tester and check the battery several times a year. Use the battery manufacturer instructions for testing along with the instructions for the tester.
• Periodically inspect the battery cables and the terminals for corrosion or bulging.
• Check the battery box and vicinity for corrosion and leaks. Make sure the box is a good fit for the battery if you use one. Make sure the hold-down hardware is doing its job.
• Make sure your charging system is in good shape. A faulty voltage regulator or slipping alternator belt will wreak havoc with battery charging.
• Don’t let your airplane sit in storage without removing the battery and placing it on a maintainer. This also protects the battery from gremlin electrical loads (the little guys that run around the inside of the engine compartment using your battery for parties).
• Don’t allow a discharged wet lead-acid battery to freeze. The sulfuric acid (H₂SO₄) turns to water, the water freezes, the plates expand, and then bulging and cracking occurs.

Taking Care of Your Lithium Battery

Lithium-ion and LFP aircraft batteries are nearly maintenance free. If you purchase one, read all the manufacturer instructions that came with it. Install any associated electronics (battery management system) according to instructions.

• Use the charger/maintainer that the manufacturer recommends. For example, EarthX sells its own battery tender for its products. The same reasoning applies here as I mentioned above for lead-acid batteries. They are not the same as automotive batteries, and if you’re going to spend the extra money for lithium, why not max out the healthy lifespan? The other reason for using the manufacturer’s recommendation is to make sure you and your airplane don’t end up in the same headline as the electric bikes with charging gone awry.
• Take the battery out of the airplane for long-term storage and follow the manufacturer’s instructions for storage.

Safety

I’ve seen plenty of dead aircraft batteries jump-started. It may work, but it’s not a good idea. If your charging system suffers a failure and you have a failing battery, you’ve lost redundant systems reliability.

Remember that working around charged batteries can deliver a big surprise in the form of fire or mini-explosions if you lay your tools on top of the battery and short the posts. You’d be surprised how often this happens. Many wrench sizes are just about the right length to perform this exciting feat.

Should you hand-prop your dead airplane, hoping to get some recharging? This isn’t a good idea either. As safe and competent as you might be at hand propping, you’ll be taking a chance flying with a dead battery. I’ve never understood why dead batteries seem to produce airplanes that are hand-propped with nothing securing them from immediately leaving.

Install a good battery box or hold-down. Buy the specific box or hold-downs for the battery you bought. This ensures the battery doesn’t come loose and knock about the installation area. Even if the battery is sealed, vibration and hard knocks are not good for it.

Recommendations

Consider making your next aircraft battery a sealed lead-acid if you are still using a wet-cell type or upgrading to a lithium variant.

Invest in a battery maintainer designed for your specific battery, and use it when you’re not flying. Short flights (less than a few hours) may not bring the battery to where it should be, shortening its potential lifespan.

Read and follow all the instructions that came with your battery and charger, and store these in a safe place with your other maintenance information.

At the annual or condition inspection, don’t skip testing the battery capacity and checking bus voltage. Make sure the voltage regulator is exactly where it should be. Over- or under-charging will shorten battery life.

Modern batteries combined with thoughtful care can save you from the dead battery surprise moment we hate so much.

Lisa Turner, EAA Lifetime 509911, is a manufacturing engineer, A&P mechanic, EAA technical counselor and flight advisor, and former designated airworthiness representative. She built and flew a Pulsar XP and Kolb Mark III, and is researching her next homebuilt project. Lisa’s third book, Dream Take Flight, details her Pulsar flying adventures and life lessons. Write Lisa at Lisa@DreamTakeFlight.com and learn more at DreamTakeFlight.com.

Post Comments

comments