Like Schrödinger’s cat, a battery is both alive and dead at the same time. When found alive, the expected state, life moves forward as planned. When found dead, the immediate future is cast into disarray. Your day takes a new direction. Disappointed passengers are disembarked. Flight plans are canceled. Troubleshooting begins. Cowls come off. Wires get wiggled. Jumper cables are sought. It’s really no fun.
If you’ve ever owned a battery, you know they die or are found dead only when you need them. Knowing batteries fail, however, arms us with knowledge that can reduce the odds of a failure and minimize the failure’s impact.
Master Switch—Off
Let’s start here, so to speak. Turn the master switch off. It’s easy, it’s a checklist item (or should be), it’s a common cause of dead batteries, and it’s 100% preventable.
Battery Maintainer
The second line of defense against a dead battery is to keep it suckling on a battery maintainer. Not a charger, a maintainer. An old-fashioned battery charger simply force-feeds amperage into a battery that may be in no condition to accept it. You may get one start, or a few, which may be all you need to get home, but it’s doing an already damaged or depleted battery no favors.
A maintainer, however, is a holistic approach to battery care. They don’t just force amperage into a depleted battery; they nurse the battery so it can accept a charge and hold onto it. You won’t find a “Start” switch position on a maintainer. You won’t find any switches at all—only lights that tell you what it’s doing to the patient at any given moment, and an implied request for patience until it shows all green.
One important service a battery maintainer can perform is desulfation. Left sitting, lead-acid batteries develop lead sulfate on their plates. The lead sulfate converts back to lead, lead oxide, and sulfuric acid when a battery is charged. But a battery that remains unused for a long period develops a more stable lead sulfate crystal, which permanently degrades the battery. Maintainers can desulfate a battery that has been sitting and prevent the condition from returning. My Sonex, with an Odyssey battery, was plugged into a maintainer 24/7. My garage is full of limited-use batteries—large and small—and each is kept healthy with a maintainer, even through Wisconsin’s gray, soul-depleting winters.
Lithium batteries have special charging needs to keep the cells balanced. If you are among the growing population of people using a lithium battery, make sure the maintainer you chose is appropriate to the battery. The battery’s manufacturer is the place to look for a recommendation.
Jumper Wires Hardwired to the Battery
When the day comes to jump a battery—and it came for me once, at Sun ’n Fun, when I ran my battery down trying to get water to combust—it’s nice to be prepared. That preparation comes in the form of having a simple way to jumpstart the battery. I equipped my battery with a drop-cable from the battery’s positive terminal and made it accessible through the cowling’s exhaust outlet, so a jumper could be attached without having to remove the cowl. The free end of the cable had a terminal ring crimped to it, which I protected with a short length of snug-fitting rubber hose. The negative cable of the jumper was attached to an exhaust pipe, similar to grounding the aircraft during refueling. The preventive action was easy to implement and added negligible weight.
Ultimately, a battery will fail. They are wear items, like brakes, tires, and air filters. A maintainer, however, will give your battery the longest, most reliable life possible. For more on this topic, visit my Substack page.
6 years ago, I replaced my RV-7’s Odyssey 680 with an EarthX ETX680 and popped for the Optimate charger that EarthX sells on their website. I figured that rather than wander through the Sporty’s/ASpruce/Amazon jungle of chargers I’d get the one the manufacturer recommends. I recently performed the 80% capacity test listed on the EarthX manual and the battery passed the test handily.
Good article and information. Most aircraft builders do not install an external power receptacle on their aircraft. However, it is a very inexpensive and extremely useful addition, either during the build or retrofit. This kit makes it easy (https://whitelightninggpu.com/products/bm-aik2b) and can be wired up two ways. Disclosure: My company makes this product. Also, if you want to know more, here is a free resource, white paper on battery maintenance charging. https://cdn.shopify.com/s/files/1/0626/5372/6871/files/Aviation_Battery_Maintenance_Article_20250522.pdf?v=1748031809
I have battery tenders on my 24 volt Cessna 180, my 12 volt Best Tugs tug for the 180, and the 12 volt batteries in my gyro plane and 4-wheel ATV in the hangar. For the plane and gyro I use power strips for multiple chargers and engine/oil heaters.
Each is connected to a wifi smart outlet and I can turn them on before flights on cold mornings and also via schedules for automatic maintenance for those less used items.
The C-180 has an external power port and I connected a pigtail directly to the battery (under the aft baggage compartment floor) for easy connection when putting the plane away.
I’ve used a BatteryMINDer, the brand recommended by Concorde, for 20+ years, and have had a good experience. For most of us, infrequent use of the airplane, and secondarily keeping the battery charged and free of sulfation is the challenge. For those of us with private hangars, the chargers are cheap insurance that the battery will be ready for the next flight, and you may also have longer battery life.
Note, Concorde came out a few years ago with a policy that they no longer recommended continuous use of battery maintainers. They indicated that they could deplete the battery’s water, even for AGM models like the one I use, while in maintenance mode over many months, followed by plate corrosion. They won’t come out and say that their concern is for certain maintainers over others, or that the policy does not apply to the BatteryMINDer that they worked with VDC to develop to Concorde’s specifications. When I spoke to one of their engineers, for the RG (recombinant gas, ie. absorbed gas mat (AGM)) they recommend topping off with battery after flight for 24 hours and then returning to the hangar to remove the charger and leave it off between flights as long as it is less than a month or so between flights. That can be inconvenient. I did that for a year or two after the recommendation. Then I went back to continuous charging. I’ve always gotten 5-6 years of battery life from my Concorde batteries, and that’s pretty good considering I live in the hot Southeast. Batteries have become expensive, but compared to everything else on the airplane, are still relatively cheap, and I consider them a wear item. I want it to be fully charged when I am ready, in good health, and to have rated capacity in the event of an alternator failure (though, with my IO-550, I will make a landing at the nearest field since my alternator is direct drive and alternator failure might in some cases cause an engine failure).
Here’s some notes and links I have about continuous battery maintainers from Concorde:
The exceptions to continuous charging mentioned are 1) parasitic drain with inability to disconnect the battery between flights and 2) use of the aircraft only once or twice per month with it being inconvenient to apply a charger for 24-48 hours before flights.
Concorde’s technical paper (#15) on maintenance charging was published in July 2023. (https://batterymanagement.concordebattery.com/BatteryDocs/TB15.pdf).
This is from their FAQs:
The rate of self-discharge of RG Series batteries is only 2-3% per month at room temperature. Maintenance charging is only recommended if your aircraft does not accumulate many flight hours per month, flies short legs that do not allow the battery to fully recharge, or has a parasitic load when the master power switch is turned off. In these cases, the battery should be periodically boost charged in accordance with the CMM. Alternatively, an approved maintenance charger may be used for supplemental charging. When a maintenance charger is used, 24/7 charging is not normally recommended and may actually reduce the battery’s life. A weekly or a monthly charge for 24-48 hours is normally sufficient when using a maintenance charger. For more information please review Technical Bulletin 15.
Maintenance chargers should include a 3-stage charging profile that includes a bulk stage (current limited), absorb stage, and float stage. The recommended voltage settings at room temperature are 14.125 ± 0.125 (28.25 ± 0.25V for 24-volt batteries) in bulk and absorb stages and 13.2-13.4V (26.4-26.8V for 24-volt batteries) in float stage. These voltage settings should be compensated for using a temperature coefficient of -0.024V/°C (-0.048V/°C for 24-volt batteries). Concorde has tested various models of maintenance chargers and recommends the use of BatteryMinder S5 models (i.e., 128CEC1-AA-S5 for 12-volt batteries and 244CEC1-AA-S5 for 24-volt batteries). If other makes/models are contemplated, contact Concorde for our recommendation.
Here’s a link to Concorde’s technical paper on parasitic loads and how to measure it: https://batterymanagement.concordebattery.com/BatteryDocs/TB10.pdf
Great info and a nice reminder that battery technology and maintainer technology are always changing. Just as we used to jolt a dead battery back to life with a 100 AMP jump start, today’s technologies and techniques are not forever technologies and techniques. Another reason that a battery manufacturer is the best resource for recommending a specific maintainer for their battery.