From our own ownership experience, satisfaction surveys, and maintenance shops we talk with, aircraft batteries commonly last two to three years for what we think is reliable operation. A reliable and useful service life includes an emergency mode of operation—call it 30 minutes of reserve capacity to operate the aircraft’s systems and avionics—with minimal loads after shedding nonessentials. There are some exceptions to useful life, of course, and a lot of that has to do with how you store the battery, the climate in which you operate, and even the brand of the battery. We’re preparing a fresh battery survey to get some feedback on brands, performance and reliability. Stay tuned. In the meantime, treat your battery right, and don’t assume it’s completely healthy. Herewith are some tips for getting the most out of its generally short useful life.
Is It Healthy… Really?
The thing is that batteries can offer a false sense of security—still cranking a high-HP engine like nobody’s business—but quickly run out of juice when the alternator fails in flight. For some this may be an acceptable risk for fair-weather VFR flying, but for us it just doesn’t make sense when it comes to safety and convenience. And when it comes to aircraft batteries, forget what you know about traditional automotive batteries.
The first issue with aviation batteries is the marginal size and capacity for the job because the goal is always to save weight. Lithium batteries are an exception, weighing far less than lead-acid models, but not everyone has adopted them. Shops and suppliers tell us they still sell far more traditional Gill and Concorde batteries (to name a few) than the latest models from the good-performing EarthX and True Blue Power, to name a couple more.
Regardless, aviation batteries are much smaller with less capacity than an automotive battery, yet they are required to start an engine with often twice the displacement of an auto engine, filled with oil that’s thicker to churn through. This means the aircraft battery discharges more of its capacity to start an aircraft engine than the typical starting chore for an automotive engine. Batteries for turbine aircraft are a different story altogether. For our purposes here, we’ll stick with piston applications.
Unnecessary Roughness
It’s a given fact that the more deeply you discharge a lead-acid starting battery beyond a very minimal starting burst, the shorter its life, with all other things being equal. Next, being a chemical beast, a lead-acid battery slowly self-destructs, which is made worse from disuse as it self-discharges with the simple passage of time. The process is called sulfation and is essentially a decrease in usable battery plate area and thus capacity. Frequently, the battery is not fully charged because of short flights or even worse, ground runs for the sake of running the engine during long periods of storage. For engine and battery health, it’s often better to not run the aircraft at all unless you’re going to fly it. Too many times, the battery sits idle between flights in an already partially discharged state. And the more time a battery spends partially discharged the faster it becomes permanently damaged by sulfation and loses capacity.
AGM batteries contain a special glass mat separator that wicks the electrolyte solution between the battery plates. The material enables the fiberglass to be saturated with electrolyte, storing the electrolyte in a suspended state instead of in a free liquid form. Sealed AGM batteries do have greater resistance to self-discharge while sitting unused, but that does not seem to have greatly increased its useful life when used the same way an old-fashioned flooded battery of the same capacity is used. Sitting unused is destructive to both battery types, causing capacity loss, just at a slower rate. In general, it commonly takes two hours to recharge a battery during flight with a properly adjusted charging system. And charging system voltage that is either too high or too low will slowly and permanently damage a battery and shorten its useful life.
The Wrong Charger
There’s more. The way we see it, the worst thing for a battery is not connecting it to a battery tender when the plane is not flown at least once every few weeks. In exceptionally cold climates, we’d plug it in all the time. We learned the value of battery tenders years ago with motorcycle batteries, plugging them in—all year—and generally get five years of useful life from each battery when stored in an unheated garage in New England. But the next worse thing is using the wrong battery charger, which can be more damaging than not using a charger at all. First, high battery voltages are bad—even the typical 10-amp auto charger tends to have too high a voltage for an aviation battery. Also, prolonged charging (call it longer than overnight) with voltage that’s over 13.3 (26.6 in a 24-volt system) in a trickle-charge mode means the battery will slowly dry out and sulfate.
If it’s a flooded battery and the electrolyte stays above the plates, you can add water. If it’s a sealed battery, the damage from abuse is permanent. Dig deep enough into the literature and you find that even so-called smart automotive battery chargers have voltage that often peaks too high, with trickle charge voltages that are above the recommended levels for aviation batteries.
Arguably, this is particularly an issue with sealed aircraft batteries, and according to shops we talked with and prior surveys we’ve produced, some battery models have proven more susceptible to damage from elevated charging voltages. In the end, if you want to maximize battery life, keep the aircraft’s charging system properly adjusted to at least 13.9 volts and below 14.5 volts (in a 12-volt system) and use a battery tender designed for aircraft batteries, if not a maintainer with a trickle charge that’s under 13.3 in a 14-volt system and 26.6 in a 24-volt system. Aircraft charging systems are one of the more neglected systems on the aircraft and are the cause of more battery issues than necessary. So is the aircraft battery box and cables, which take a beating from vibration and the general duties imposed on it containing a battery.
One reliable battery tender model we’ve used is the aircraft-specific BatteryMINDer from VDC Electronics, which is a three-mode charger/maintainer/conditioner that won’t overcharge the battery. It’s proven on sealed or wet-cell aircraft batteries and is spark-proof, has short-circuit protection, and has temperature compensation. Sporty’s sells the 12- and 24-volt model for under $300, plus it offers a hardwire kit for quick plug-in and disconnect. Another useful hangar tool is a portable ground power unit. We’ve used the White Lightning aviation ground power units and are impressed with their efficiency, reliability, and performance, and the latest models have built-in VDC BatteryMINDers and a smartphone interface for remote use.
We’ll look specifically at upkeep as it relates to lithium aircraft battery tech in an upcoming report in Smart Aviator.
Our appreciation to Jonathan Sisk for sharing his White Paper that offers sound guidance on aircraft battery care and longevity. We think it’s worth reading. Download “Aviation Battery Care and Longevity”.
On battery maintenance: Battery Tender is a trade name.
Battery Minder is the trade name of the VDC Electronics battery maintaner, which is bespoke designed for our aircraft batteries, and uses desulfating technology to recover and prevent desulfation. I’ve used one for 15 years; it sustained a Concorde for 9 years until a mechanic ran it totally flat failing to start my engine after maintenance; the successor Concorde had suibnormal capacity from the beginning and lasted 4 years with this charger.
That’s right. The Deltran Battery Tender product was perhaps the first trickle charger, and the company has been around since the 1960s. The “tender” became a household name.
Wet cell or AGM–I’ll take AGM thank you.
I have mixed feelings about trickle charging 24 x 7, but also understand the philosophy behind the lower voltages in the ‘Aviation’ BatteryMinder. I refused to pay the ‘Airplane tax’ on those chargers – it’s the same as one of their automotive charger models just with different voltages and an extra $150 tacked on!
I bought a TopDon TB6000pro which is a sub-$100 bluetooth enabled smart charger. It enables the user to program custom charging profiles. I made my own programs with the lower voltages as specified in the ICA for my Concorde battery. I rarely leave it charging unattended.
Thanks for the good info. Glad you guys are back to writing great and useful content.
Great summary! Did I catch a typo? 13.3 not 12.3.
“not a maintainer with a trickle charge that’s under 12.3 in a 14-volt system and 26.6 in a 24-volt system”
good eye—now someone get Anglisano more coffee.
I’ve used a Battery Minder for Concorde AGM for 20 years. I agree with the post above that I used to get longer life, was getting 6 years even living in the deep South where heat lowers battery life. For the last two batteries, I’ve only gotten 3-4 years. Concorde says there have been no design changes…but I have heard many folks getting 7-9 years in the past that are getting only 3-4 now.
My last Concorde 35-AXC would pass a capacity test just fine, but the cranking amperage was low after only 3 years, which was obvious when starting. Still, I think Concorde AGMs are the best option for most of us. At present, Lithium does not make sense to me financially, and despite all the electronics, etc. I’d rather have no risk than a very low risk of a battery fire. Saving a few pounds is not worth thousands of dollars to me.
Concorde has recommended against continuous use of battery maintainers, even the Battery Minder brand that they worked with to charge and maintain their batteries. I’ve done that for 20 years and my situation is unchanged (hangar, airplane, hours of use, etc.). I’ve purchased several Battery Minders over the years as they’ve optimized the settings for Concorde.
Concorde recommends fully charging the battery for 8-24 hours after flight and then disconnecting the charger if there is no current leak on the battery with everything off. I’ve got a digital clock in my yoke that gets power from the ship’s battery). Concorde says that even in the Battery Minder’s maintenance mode, there is a chance one could use up electrolyte over time and shorten battery life. They recommend fullycharging every month or so if not flying regularly, time between charges dependent on temperature.
I did that for a while, but if you’re not flying that often, that is a pain. Plus, you have to go to the hangar the day before the flight to top off the battery.
I’ve had good battery life over 20 years using the Battery Minder continuously. Despite talking to Concorde techs and listening to their FAA presentation in the last year saying they do not recommend continuous Battery Minder use, I am using mine continuously in the hangar. I think Concorde added this recommendation partially because they don’t know what type of charger you are using (and regular, low tech, trickle chargers used continuously definitely can shorten life).
Batteries aren’t cheap, but I am not convinced that continuous maintenance mode is lowering my battery life.
Ya snuck this one in on me while I was typing the next comment, Justin 🙂 I agree 110% with your assessment. The selection of battery charger IS important but if you’ve done it right, leaving a battery sitting at 0.4 volts above its fully charged open circuit value 24/7 should not harm it at all. I use cheap Harbor Freight trickle chargers as well as a few other HF types. They USED to make what I call a ‘ramp charger’ … no longer available. This charger takes the battery up to 14 volts then turns off until it senses it floated back down to 13.0 volts then turns on again. I have two vehicles parked for 6 months at a time on those hooked to a timer. For 3 hours/day, that ramp charger comes on, does its thing and is then turned off. Both 3 year batteries are now 7 years old and working fine. When I get back … the vehicles start right up.
BTW: I ONLY use the maroon batteries in my airplanes.
GREAT general info, Larry. As a long time A&P, multiple aircraft owner and retired USAF type, I have cared for hundreds of batteries over the years. I can attest to the fact that letting a battery sit in a partially charged state OR having a parasitic load on it slowly draining it is the main cause of early battery failure. Heat makes it worse.
I leave many batteries in all sorts of vehicles and airplanes sit for long periods of time but each and every one of them has some sort of hand-picked charger on it, most running 24/7. Batteries don’t know what the source of the electrons being pumped into them is … or care. Paying big bucks for some gee whiz charger is nuts … as mentioned above. The main thing is to keep the battery ABOVE it’s open circuit voltage when it’s fully charged … but not too far. Your 13.3 or 26.6 volt value is exactly what I tell people. Everyone should REMEMBER THOSE VALUES. So, for example, a 12 volt battery, brand new and fully charged should measure ~12.9v after sitting for 30 min. Keeping it 0.4 volts above that value is what gives the battery long life and good service. Any constant charging above those values is harmful.
I have a Ford F250HD that I rarely use. I keep a hand picked low buck Harbor Freight trickle charger on it which puts out 13.35 volts. That battery sits 24/7/365 with the charger on. The first battery lasted 10 years. The second battery lasted — are ya ready — 18 years. I routinely get at least twice the manufacturers warranty period out of each and every battery I care for.
I have a better 10 amp charger where I can select constant voltage or constant current modes. Every now and again, I hook batteries to it and give ’em a good bulk charge in constant current mode then hook up to whatever trickle charger I’ve selected for them. You can ‘fry’ a battery pretty fast in constant current mode so ya have to be careful. MOST chargers operate in constant voltage mode which isn’t quite as bad. I can monitor the charging current on that charger, as well. That’s another ‘secret.’ Batteries in good condition being trickle charged with a constant voltage charger 13.3 v should float down to near zero charging current as its internal resistance changes due to the charging.
Lastly, the source of the battery is also important. Batteries made out of recycled lead do not last as long as a battery made of pure virgin lead. There aren’t many sources of lead so most are made using recycled lead. I often joke that I don’t buy batteries made out of ground up WalMart lead 🙂
I flew out of the low hot deserts of the Southwest, and I almost never got more than 2–3 years from a 12- or 24-volt batteries. Heat just kills them. There’s an industry-wide rule of thumb that every 15°F over 77°F cuts life in half, and in my experience that’s about right, didn’t matter which brand or charger I used.
That’s exactly why you’d often find the hoods up on my vehicles after I drive, Raf. And, on my 172, you’d find the oil filler door open after a flight. Getting rid of the heat ASAP is the name of the game. Even in hot Florida, doing this helps the battery last longer.
Slightly off subject, newer cars have current monitoring capability on them. The computer knows how much power is going in or out of a battery. Quite often, if the vehicle isn’t demanding high current (headlights on, A/C on), it’ll back off on the alternator output by reducing the alternator excitation voltage. They do this to slightly increase fuel mileage. Individual car owners don’t notice it but the Corporate Average Fleet Economy (CAFE) values are important so they chase any and all places where they can improve CAFE for Uncle Sammy. I found this out because I have the habit of commanding my headlights off during the day. I plugged in a voltmeter and was aghast to find low bus voltage by doing that.
This is why I tell airplane owners — especially those with an airplane that have a load meter (1/2 of an ammeter) to install a voltmeter in their airplanes. Keeping track of bus voltage is important. And load meters only tell “load” … not charge current. Everyone should have a voltmeter in their airplane. These days, numerous instruments have a voltage monitoring capability so its easy to do. I had a Piper Cherokee with a load meter that was charging but not enough to keep the battery happy. The batteries weren’t lasting and I finally traced the problem to a dying voltage regulator. I replaced that but also added a voltmeter. Problem solved. The EI VA-1 instrument is a good choice.
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All good comments and an excellent topic for discussion. Is there an incentive for manufacturers to make longer lasting batteries? probably not. Consider the abuse the average car battery gets regarding heat, over/under charging, draining, physical abuse riding on gravel roads and potholes, jump starting other vehicles etc. They do pretty well. The manufacturers could do much better. I do have a voltmeter in all my road machines and the aircraft. Good advice.
Just yesterday, I flew with my buddy who has an older PA28-140. Having ONLY a loadmeter was a ridiculous design error on the part of Piper. I don’t even know what the heck it’s helping you to know. Unless something has a short and is drawing very high current, the loadmeter serves no purpose. An ammeter at least tells you that you have a positive rate of charge after starting and in flight. I have several plug-in voltmeters in my toolbox that I can plug into a cigar light socket to determine bus voltage IF the airplane doesn’t have any other way of determining what it is.Again, I urge ALL airplane owners to have a voltmeter capability in their airplanes. Some airplanes have an over voltage circuit to protect avionics from a runaway charging system along with a warning light but unless that happens, you could be seriously under charging your batteries and not even know it.
I found out that there are only two main sources of pure lead in the western hemisphere. One in MO and another in Mexico. I discovered that batteries that use pure new virgin lead last longer but manufacturers like to use the reclaimed stuff … hence why some batateries don’t last.