KZNY Posted Tuesday at 01:50 AM Report Posted Tuesday at 01:50 AM The aircraft was flown 10 days back and over the weekend, as part of pre-flight, we tried to turn on the Master switch to check flaps, nav lights etc. However the Master Switch on/off pretty much had zero impact. The switch didnt seem to have any contact issues. We thought it was a dead battery (due to extreme cold temps here) and measured the voltage at the battery, it showed 0.4V. Today the AMP pulled the battery out and he reported the battery was still 22V. However during our check yesterday, the battery did measure 0.4V. While the AMP is going to look at it tomorrow and check it all out, I was curious if anyone has experienced, observed something like this or thoughts?
LANCECASPER Posted Tuesday at 02:04 AM Report Posted Tuesday at 02:04 AM 12 minutes ago, KZNY said: The aircraft was flown 10 days back and over the weekend, as part of pre-flight, we tried to turn on the Master switch to check flaps, nav lights etc. However the Master Switch on/off pretty much had zero impact. The switch didnt seem to have any contact issues. We thought it was a dead battery (due to extreme cold temps here) and measured the voltage at the battery, it showed 0.4V. Today the AMP pulled the battery out and he reported the battery was still 22V. However during our check yesterday, the battery did measure 0.4V. While the AMP is going to look at it tomorrow and check it all out, I was curious if anyone has experienced, observed something like this or thoughts? Is your battery a Gill or Concorde? According to the logs how old is it?
KZNY Posted Tuesday at 02:07 AM Author Report Posted Tuesday at 02:07 AM 2 minutes ago, LANCECASPER said: Is your battery a Gill or Concorde? According to the logs how old is it? Its a Gill Battery with the install date of Jan 2024. Just short of 2 years by 2 months.
LANCECASPER Posted Tuesday at 02:22 AM Report Posted Tuesday at 02:22 AM 19 minutes ago, KZNY said: Its a Gill Battery with the install date of Jan 2024. Just short of 2 years by 2 months. The last Gill I bought lasted 20 months. I inquired about the pro-rated warranty. They were going to give me a $100 credit if I bought another Gill. Not a chance. It sounds like you have a dead cell. You don't need an A & P to change out your battery. Highest chance is that it is the simplest thing - a bad battery, especially since it's a Gill.
KZNY Posted Tuesday at 02:34 AM Author Report Posted Tuesday at 02:34 AM 11 minutes ago, LANCECASPER said: The last Gill I bought lasted 20 months. I inquired about the pro-rated warranty. They were going to give me a $100 credit if I bought another Gill. Not a chance. It sounds like you have a dead cell. You don't need an A & P to change out your battery. Highest chance is that it is the simplest thing - a bad battery, especially since it's a Gill. Would it measure 0.4V when the battery was connected in the aircraft and then measure 22V when pulled out? I dont know what load could be on the battery when the Master switch is OFF.
LANCECASPER Posted Tuesday at 03:00 AM Report Posted Tuesday at 03:00 AM 28 minutes ago, KZNY said: Would it measure 0.4V when the battery was connected in the aircraft and then measure 22V when pulled out? I dont know what load could be on the battery when the Master switch is OFF. If it's at 22 volts you're probably not going to recover the battery. Has he tested your battery relay? What model/year Mooney do you have? Is there a baggage light? Was it left on?
KZNY Posted Tuesday at 03:07 AM Author Report Posted Tuesday at 03:07 AM 5 minutes ago, LANCECASPER said: If it's at 22 volts you're probably not going to recover the battery. Has he tested your battery relay? What model/year Mooney do you have? Is there a baggage light? Was it left on? It's a 1998 M20J. I am not sure if any of the lights were left one. However will it measure 0.4V when in the aircraft and then 22V when removed?
LANCECASPER Posted Tuesday at 03:11 AM Report Posted Tuesday at 03:11 AM 5 minutes ago, KZNY said: It's a 1998 M20J. I am not sure if any of the lights were left one. However will it measure 0.4V when in the aircraft and then 22V when removed? A very common thing on 90's Mooneys is that the switch in the baggage compartment gets bumped after taking out luggage after a trip and the battery dies and gets to a low point where it can't be recovered. I did it once on a '96 Mooney Bravo. Later on Mooney wired in a delay circuit which turned the light off after 10 minutes. I would be surprised if a new Concorde battery didn't take care of your problems.
MikeOH Posted Tuesday at 03:36 AM Report Posted Tuesday at 03:36 AM (edited) Put a small load on the battery when out of the aircraft; maybe a small 28V bulb. If the voltage collapses you'll know it's the battery. Edited Tuesday at 04:25 AM by MikeOH Changed to 28V 2
PT20J Posted Tuesday at 03:49 AM Report Posted Tuesday at 03:49 AM 22 V open circuit voltage would be a 0 charge state. In a M20J, there are overhead lights connected to switches in the overhead. These are wired directly to the battery and will deplete it when left on. If the battery is dead, it might show 0 V in the airplane if the switch to the lights is still on. After removing the battery it might recover a bit which might be why it showed higher voltage outside the airplane. The test @MikeOH suggested would confirm. You can try charging it and then performing a capacity test to check the battery’s health. However, as others have said, Gill sealed batteries don’t seem to last long and your best bet might be to replace it with a Concorde. 1
NotarPilot Posted Tuesday at 05:50 AM Report Posted Tuesday at 05:50 AM I switched to Concorde from Gill after buying my plane. Never had an issue. I tend to replace them after 4 or 5 years regardless if I feel they need replacing. This is probably a bit premature on my part. 1
rgpilot Posted Tuesday at 12:07 PM Report Posted Tuesday at 12:07 PM Check the ground hook up from the battery to the aircraft. I had similar problem caused by the connection to the aircraft from the ground side of the battery.
Fritz1 Posted Tuesday at 02:42 PM Report Posted Tuesday at 02:42 PM as stated before most likely battery is dead and the load that killed it is still on, internal light wired directly to the battery, these lights are hard to see in bright daylight, I close the hangar door and as a last check and look into the cabin to verify lights are off, replaced both my Concords last year, died within 6 months of each other, 6 years and 6.5 years old, expensive but think overall still best battery
LANCECASPER Posted Tuesday at 03:30 PM Report Posted Tuesday at 03:30 PM 13 hours ago, KZNY said: It's a 1998 M20J. It helps if you put that on your profile, that way on any questions you ask the answers can apply to your airplane. You have a very special airplane. Your Allegro is one of the last 19 J models ever made, having all of the continuous improvements over 22 years of production.
KZNY Posted Tuesday at 04:10 PM Author Report Posted Tuesday at 04:10 PM 39 minutes ago, LANCECASPER said: It helps if you put that on your profile, that way on any questions you ask the answers can apply to your airplane. You have a very special airplane. Your Allegro is one of the last 19 J models ever made, having all of the continuous improvements over 22 years of production. Done. Thanks for the tip.
LANCECASPER Posted Tuesday at 04:45 PM Report Posted Tuesday at 04:45 PM Friends don't let friends buy Gill batteries. Concorde has two sizes that will fit your airplane, the RG24-11 and the RG-24-15. You don't need the vented version (it has an "M: as a suffix), but you can use either version. Since you only have one battery on a J model it makes sense to buy the one with the best amp rating, the RG24-15. Chief Aircraft has the best price when you consider they cover shipping and they don't collect tax. A shop is going to charge you full retail on the battery. You can easily change this yourself, although you may need some help safety-wiring the hold down. You can buy the RG24-11 for $749 or the RG24-15 for $899.
Fly Boomer Posted 23 hours ago Report Posted 23 hours ago On 12/8/2025 at 7:50 PM, KZNY said: We thought it was a dead battery (due to extreme cold temps here) and measured the voltage at the battery, it showed 0.4V. ............ While the AMP is going to look at it tomorrow and check it all out, I was curious if anyone has experienced, observed something like this or thoughts? I can think of a few times. How did you [measure] "the voltage at the battery"?
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