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Let's get the collective wisdom rolling My M20J is fresh out of the avionics shop after installing a G3X panel. Last week when I flew it, the R wing fuel gauge stopped working. Well the fuel senders are old and I am contemplating a switch anyways. The very next flight, when I tried to start the engine I turned the key the plane seemed like the battery was low. I thought it was odd but maybe I spent a little too long updating the navdata with the engine off. I started it with an external source and went flying. Everything seemed normal so I took it on a 2hr XC flight. Today, flying back home I experienced the same behavior and had to use and external source to start up. Now, both COMM radios had an interference of a quick rhythmic "popping" sound. Additionally, in cruise I could see the ammeter was showing some crazy readouts, going from -30 to -290 amps!!! After I landed the ammeter showed a reasonable +2 amps. I tried turning on and off various systems and lights to see what I could find but no clue. Nothing particular happened. I suspect something is shorting the system and draining the battery. Perhaps the fuel sender line (it may have nothing to do with the electrical problem but what the hell)? Any thoughts? Here are some pictures.

Hi guys, For some time now I've been struggling with a problem with my electrical system. I own a 1977 M20J. It all started 8 months ago. All of the sudden after annual, my battery started to lose its charge in a matter of days. Literally after 3 days of staying in hangar, it would be so depleted that it wouldn't start anymore. After some troubleshooting we determined that the battery was old and thus it was losing its charge. I replaced it and everything worked great for some time. The longest lasted without flying was 2 months and it still had 12v precisely. A few weeks ago the problem started all over again. It started to lose power to a point where after two weeks it wasn't able to start-up, then one week, then 3 days and now it's hard to start it normally after 8hrs... It can be relevant that 2 weeks ago my alternator stopped working mid flight and was allegedly repaired by a mechanic in a foreign country. Nothing I did with the breakers or anything did anything mid flight. We checked the battery once again but it turned out to be perfectly formed and not missing any electrolyte from any of the cells. Do you guys have any idea what could be wrong? Has anyone encountered a similar problem in the past? Any suggestions? Best regards, Wojciech Kacprzyński, A fellow Mooney owner

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From AIN: Self-charging Diamond Batteries Set To Power Aircraft by Charles Alcock August 25, 2020, 10:06 AM NDB is developing a self-charging nano diamond battery that it says will be able to power electric aircraft. [Image: NDB Inc.] California-based startup NDB claims it is poised to offer a diamond-based alternative to current battery technology that will be more efficient and sustainable for electric aircraft. On August 25, the company announced it has completed proof-of-concept tests on its self-charging nano-diamond battery, achieving what it claims is a breakthrough 40 percent charge, compared with charge collection efficiency rates of just 15 percent with commercial diamonds. NBD also announced it signed two undisclosed launch customers—an aerospace, defense, and security manufacturer, and a Europe-based nuclear fuel cycle products company—for a beta version of the technology. Electric aircraft and vehicles are among the anticipated early adopters of the technology. The privately-owned company is now working on the first commercial prototype of its nano-diamond battery and aims to have this available by year-end. It said the proprietary self-charging process will provide a charge for the full lifetime of any device or machine, with up to 28,000 years of battery life. The power source for the nano-diamond battery is intermediate- and high-level isotopes that are shielded for safety by multiple levels of synthetic diamond. According to NDB, the energy is absorbed in the diamond through a process called inelastic scattering, which is used to generate electricity. Since the battery is self-charging, which requires only exposure to natural air, any excess charge can be stored in capacitors, super-capacitors, and secondary cells. It does not require any external power source and also incorporates a DC-to-DC converter to control the current. Additionally, NDB said, the diamond batteries do not require materials sourced in conflict zones or those that could be ecologically damaging. “A 40 percent [charge] efficiency has never previously been achieved due to [previous] material choices and our proprietary technology has achieved this breakthrough in efficiency,” NDB’s CEO and co-founder Nima Golsharifi told AIN. “What we have achieved competes with what is available from traditional fossil fuels in terms of energy density, and it is not climate- or light-dependent [like other sustainable power sources]. NDB believes it will be able to achieve a 90 percent rate of charge. This further progress could result in smaller, lighter batteries being available. The company is now engaged in research work aimed at supporting the use of nano-diamond batteries to power eVTOL aircraft. The work is supposed by the U.S. government’s defense and energy departments. Meanwhile, NDB also has been working with eVTOL developer Bartini Aero to explore the possible use of nano-diamond batteries for its planned autonomous vehicle. Previously, Bartini has intended to power the design with hydrogen. According to Golsharifi, the batteries will provide sufficient power to support cruise flight for unmanned aircraft. The company expects to build a commercial prototype of the battery within the next three years. It said that the diamond that encases the isotopes are more than 11 times stronger than the materials used for battery cases and able to withstand temperatures of up to 3,632-deg F. The proof-of-concept testing was conducted at the Lawrence Livermore National Laboratory in the U.S. and at the Cavendish Laboratory at the UK’s Cambridge University. Experiments were led by Professor Sir Michael Pepper, a pioneer of semi-conductors and winner of the Institute of Physics Isaac Newton Medal. This story comes from the new FutureFlight.aero resource developed by AIN to provide objective, independent coverage, and analysis of new aviation technology, including electric aircraft developments.

Hi folks. Just bought a 1974 M20F. Love it after only 10 hours of flight, but I have noticed something unusual with the battery charging system. Every once in a while the battery alert comes on in the jpi 700 and the auto pilot turns off due to insufficient charge. Concord battery is 2 years old. Checks out at 13.07 volts standing charge. Jpi 700 shows between 13.4 - 13.6 charging in flight, now that I’m watching it. I’m assuming my alternator is going out since I think I should see 14+ volts, but I don’t know whats normal. Thoughts?

In the winter I had a new battery installed because it was dead and would not take a charge. (1998 - m20m ) . it was replaced with a brand new one. I thought it was just the cold or a faulty battery Today, in the heat of summer the new no-1 battery was dead and I had to start the engine on #2. ( which was successful ) Something is draining my #1 battery with the master off. I can swear that everything is off I can start the plane on #2 . no problem ( i then switch back to no#1) which I hope is an ok thing to do. After running the plane for about an hour the #1 will start the plane again Has anyone experienced this ? The only thing that I can see that remains on after the master is off is the factory little clock. but I would have a hard time believing that that would drain the battery , but I could be wrong. Thoughts. Pete

I have a Gill G-35 battery in a 201. The hangar in which the plane sits is regularly 100-120 degrees this time of year. I keep the water topped up and use a battery minder. Is there anything else I can do to keep the battery from getting torched?

Hi all, Just bought an 96 Ovation, have only flown it about 4 flights so far and loving it. I'm having a problem with this dual battery setup though, and am unfamiliar with it. Battery 2 keeps reading low volts (between 18 and 8) so I've just been running it off battery 1. I want to charge it, but don't really want to have to open up the battery access doors as I really don't know very well what I'm doing. I understand that the external charging port is wired directly to battery 1, does that mean that it will trickle-charge over to battery 2 like it does in flight if I plug it up there? Excited to become a part of the Mooney community.

Good morning everybody! My Ovation 2DX 2004 has a problem with loading battery #2.Now I examined the surrounding a little bit and found the fuse near the diodes of battery #2 blown. It's a 15A 32V glas fuse. Does anybody know about the exact function of the fuse. By the way, fuse near battery #1 was also blown! But I had never problems loading this battery. Thanks, Peter

I have a 77 201 S/N 48. Where is the voltage regulator located? Not on the firewall. Battery isn't charging and voltage is low at idle. Going to clean / check connections before I start throwing parts at it.

does anyone make a aftermarket stc, Battery box,for m20j

I have a 77 J with a 14v system. any recommendations for a new battery. thanks J

My Ovation 2, like all (?) long-body Mooney planes, has a pair of 24V batteries in the tail cone. At a MAPA training session, I was told that switching between batteries while the Master Switch was on was a bad idea as "a fuse could blow." The speaker was an experienced Mooney CFI and long-time Mooney owner. At the time I had about 4 hours of Ovation time so I just filed that away for future thought. I don't see any such warning in the POH. I've looked through the schematics and can't figure out where this "prohibition" comes from. There are two "Master" relays in the plane, and the Master Switch wire is routed to the battery selector switch which controls which of the two is connected when the Master Switch is on. The alternators, when on-line, charge the active battery directly. The non-selected battery is charged through a diode D2 so it is "trickle charged" at one diode forward voltage drop below bus voltage. At least that's I how read it. Typical M20M schematic detail attached. Question: Does anyone know of a problem with switching batteries when the Master Switch is on, with or without an alternator on-line? Or is this warning a remnant of some other model aircraft? Battery Detail Schematic M20M crop.pdf

So getting my Mooney M20C started in cold Wx is a royal pain in the six. I have engine preheating nixed for the moment, but am still struggling with the battery. If I keep it on a tender it works fine, but putting the battery box together is very difficult for me. If I leave it without a tender for even a week I haven't the power to get started. I'd leave part of a tender hanging out the battery box, but I doubt there's enough room to get anything out of there. I used to have the exact same problem with my Cherokee, but the battery was under the back seat. The voltage drop was pretty big. That said leaving part of a tender hanging out was no big deal. The battery in the Mooney is in the engine bay, not a good place for anything to hang out. Is this normal? It was for Cherokees, what about vintage Mooneys? Is my battery kaput? Is there a trick to putting the battery box back together?

One year old Gill G 243 for sale, for trade, or free to a good cause. I decided to go with sealed Concord batteries in my Bravo. Kept on a battery tender when not in use, excellent condition.

Had a strange problem this weekend..... Went to start the Mooney, flipped the Master and NOTHING! No click, no lights....Nothing! I placed the Fluke meter on the Battery and is was not reading a Single Volt.... The plane had sat for three days since my partner flew her last. All switches were off and everything appeared to be normal. I placed a 5 amp charger on the battery for an hour and she started right up as usual. The Battery was drained as I saw the Alternator doing its job making voltage and current. I stayed on the ground for an extended period of time until I saw the amperage start to back down to slightly above ZERO. All systems looked fine so I flew the aircraft on a short hop. All electrical equipment was operating as designed. I have heard a lot of Bad about Gill Batteries but in this case I think there was reason for the full discharge. My question is......Is it possible for the Relay normally activated by the Master to stay partially engaged or for the coil to stay hot? I also see a diode attached as well. Could that have created the drain? The mooney is a 1992 M20J. Any advice would be appreciated. If anyone knows how to acquire electrical diagram it would be extremely helpful. FYI.... This site has been very valuable. What a great group of enthusiast helping each other maintain their passion for these great airplanes. Even with minor problems, these aircraft have some of THE BEST engineering I have seen in a very long time! Thanks, Rick

I just purchased a one owner 1989 M20K. Low time, always hangared, mint condition. It just came out of annual, with a new battery. It sat for 2 1/2 months before I had a chance to fly it. Upon first preflight, battery only had 22 volts. Engine cranked once, but would not start. Previous owner always used a battery minder, as he did not fly much. Owner says that the battery drain is normal. My CFI says it should hold out for a few months, at least. Are any of you aware of a constant drain on the battery, and if so, what is the source and what is the fix? Thanks, this is my first post, and I look forward to the feedback.

When is best time to buy a new battery, I think mine is 2 years old. Should i buy a new one or wait till she won't start? Thoughts? I am thinking about getting a Concorde RG24-15

Need INPUT...ASAP on battery replacement recommendations! The shop working on my Rocket is saying that I need 2 new batteries (in the tail section & hard to get to) the current batteries were installed in 7/2010. I never had any problems with the batteries but they are reporting that after charging they won't start the engine.... They have quoted 2 each G-35 batteries and my cost is $245.94 each with acid. (don't know if that includes labor but if it is like the other items I doubt it...). They have also asked if I would be interested in the Concord sealed batteries! What say you? Need input ASAP so I can give them an answer! Thanks in advance, Lacee