Why are airplane batteries so Weak?

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evapilotaz

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Drone airspace abuser
Last Saturday I was testing out some new head Seats I just purchased in a C172N I rented from the Local FBO.

I may have had the coms on for 5 minutes to test everything without the engine running and shut them off before going through the before Engine Start checklist.

When it came time to Start the engine it barely cranked over. :mad2: It barely cranked two revolutions slowly and after a few tries it fired up. I got Lucky I think.

Before you all tell me to read the POH or something like that why are airplane batteries so weak in this area? I should be able to run the coms for a little while without killing the battery. Is there only a single battery in the airplane? I would assume so.

Thanks.
 
evapilotaz said:
Last Saturday I was testing out some new head Seats I just purchased in a C172N I rented from the Local FBO.

I may have had the coms on for 5 minutes to test everything without the engine running and shut them off before going through the before Engine Start checklist.

When it came time to Start the engine it barely cranked over. :mad2: It barely cranked two revolutions slowly and after a few tries it fired up. I got Lucky I think.

Before you all tell me to read the POH or something like that why are airplane batteries so weak in this area? I should be able to run the coms for a little while without killing the battery. Is there only a single battery in the airplane? I would assume so.

Thanks.
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Weight. More capacity means bigger plates, more acid (or gel), etc. All weighs more.
 
It could have been an old/tired battery. That said, the battery is something that is generally sized to be just big enough. Any more than that and it is just extra weight you have to lug around.

Jim
 
I get the weight issue but I would think I could get more run time on the battery with the avionics master switch turned on without killing the battery. I was wondering if it was normal.

Thanks.
 
Oh just wonder. What type of battery is used? Is it some Special FAA Certified Battery that cost hundreds that I could purchase at Walmart for less than $100.

I know I cannot replace the battery myself as its rented airplane. I'm assuming that an A & P has to install it and there is several more hundred in labor.
 
How confident are you that the battery is in good shape?
 
The master contactor coil draws current. The turn coordinator draws current. You might have had the panel lights turned up and not noticed it in the daylight. Then there are those radios themselves, which generally don't draw much if they're not transmitting (was the transponder on?). The beacon might have been on. It all adds up.

The battery is probably old, or has been run flat once or twice before. Killing them takes life out of them; the plates sulfate up and won't completely return to normal on recharge.

Poor cranking can also often be attributed to old or worn-out master and starter contactors. The least bit of resistance at starting currents will hold back the starter. A good mechanic will know how to take voltage drop readings across those contactors while someone cranks the engine.


Dan
 
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evapilotaz said:
I dunno. Not my Airplane. Should I bring it up with the FBO. What is normal for battery run time without engine running.
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Couldn't hurt. It has probably been mistreated.
If they are not treated well, they tend to die and can't really be brought back.

I went through this last year it just got worse and worse to the point that we were keeping a trickle charger on it at all times. It took very little to kill the battery.

I bought a new battery and I treat well and it is very strong.
 
Is the battery like your normal auto 12V battery like the one in your car or is a deep cycle marine type battery? Is it something you can service yourself?
 
evapilotaz said:
Is the battery like your normal auto 12V battery like the one in your car or is a deep cycle marine type battery? Is it something you can service yourself?
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May be 12 or 24v and it is just like any other vehicle battery.
Well except they are $500-$800 because they go in plane :(
 
An old neglected battery in a rental airplane? At least the plane started. When it gets to the point the plane won't start they will probably jump start it a few times before they get around to replacing the battery. And even then, they may just put in an old one that they have sitting around the hangar.
 
JOhnH said:
An old neglected battery in a rental airplane? At least the plane started. When it gets to the point the plane won't start they will probably jump start it a few times before they get around to replacing the battery. And even then, they may just put in an old one that they have sitting around the hangar.
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i would never rent from cheap folks that wont take care or replace a battery. makes me think how they take care of the engine. :yikes::yikes::yikes:
 
I'm sure the high summertime temperatures in AZ aren't doing the batteries any favors either. We have a car out in PHX and I swear - I feel like we put a new battery in that thing almost every other year.
 
evapilotaz said:
Is the battery like your normal auto 12V battery like the one in your car or is a deep cycle marine type battery? Is it something you can service yourself?
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spruce has mine for 259 plus tax/shipping. I'm not sure if the 172N is 12 or 24v.
 
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172N is 12V. Later models switched to 24.

5 minutes on comm should be easily handled, presuming it's light on the transmission (maybe briefly calling for fuel and getting the weather) -- though not necessary. The battery is dying. It won't be long before it won't start the engine even when fully charged and not used at all prior to start.

The big current draws are the electrical gyros (TC), flap motors, and radio transmission (reception, not so much). If there is a glass panel installed, the displays suck electrons.
 
On a Cessna with the old flashing beacon on the tail...

Largest draws are.....
1. Flashing beacon (They have a big resistor in the tail)
2. Pitot heat
3. Landing lights.
 
Invest in a handheld transceiver. You never know when that little extra bit of juice left in the battery might be the difference between starting and being stuck on a cold ramp in the winter... I try to use the battery sparingly to get required preflight tasks done (check lights, and so on); picking up AWOS, picking up a clearance, etc. can all be done via phone/transceiver or after the engine is running.

That said, it certainly sounds like the battery is getting weak. 12V batteries tend to run $200 to $300 for light aircraft and in rental use it isn't uncommon to replace them frequently. Renters tend to be hard on starters, and thus hard on batteries.
 
TUPilot said:
Invest in a handheld transceiver. You never know when that little extra bit of juice left in the battery might be the difference between starting and being stuck on a cold ramp in the winter... I try to use the battery sparingly to get required preflight tasks done (check lights, and so on); picking up AWOS, picking up a clearance, etc. can all be done via phone/transceiver or after the engine is running.

That said, it certainly sounds like the battery is getting weak. 12V batteries tend to run $200 to $300 for light aircraft and in rental use it isn't uncommon to replace them frequently. Renters tend to be hard on starters, and thus hard on batteries.
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I've been looking at those. Any recommendations in the $250 range?

Apologies for the derail.
 
evapilotaz said:
Last Saturday I was testing out some new head Seats I just purchased in a C172N I rented from the Local FBO.

I may have had the coms on for 5 minutes to test everything without the engine running and shut them off before going through the before Engine Start checklist.

When it came time to Start the engine it barely cranked over. :mad2: It barely cranked two revolutions slowly and after a few tries it fired up. I got Lucky I think.

Before you all tell me to read the POH or something like that why are airplane batteries so weak in this area? I should be able to run the coms for a little while without killing the battery. Is there only a single battery in the airplane? I would assume so.

Thanks.
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That battery was weaker than most. The thing that limits the battery power is weight, what reduces it from there is sulfation on the place surfaces. Use a charger with a desulfation circuit to prevent and remove the sulfation and return battery cranking amperage.
 
Henning said:
That battery was weaker than most. The thing that limits the battery power is weight, what reduces it from there is sulfation on the place surfaces. Use a charger with a desulfation circuit to prevent and remove the sulfation and return battery cranking amperage.
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I have one of the BatteryMinder brand chargers designed for 24 volt aircraft batteries. It will desulfate an old battery. I was able to take a dead battery that would not take a charge and get it back to life with my charger. It took a full weekend to make it happen, but it worked. Unfortunately it was the bad battery I had replace in my plane. So basically it just sits around doing nothing now.

http://www.batteryminders.com/models/

Jim
 
A fresh battery probably wouldn't have done that. Many owners don't replace until starts are a problem with or without some before start panel time.

Replacing 'on condition' takes some work. You can use a carbon pile type battery load tester to see what kind of capacity is there when the battery is loaded. You can track fully charged/no-load voltages and watch for the eventual drop of a few tenths of a volt. Both take a bit of work and record keeping. Or you can just wait for that weak start on a cold day...

You can replace on a schedule 2-3-4 years assuming normal usage and degradation.

Another approach for 'on condition', especially for IFR planes could involve running the panel with the alternator offline until something critical fails. Good thing to know if you lose an alternator... how long will you have minimum instruments before the battery discharges too much? If you want 45 mins of panel time, you can check the battery against that periodically.

I have 2 batteries and 2 alternators setup so the panel can be run on one battery and the engine started on the other. I like getting clearances and setting up the panel before the start. Especially nice if waiting for some weather to clear while sitting in the airplane at some remote airport. But SOP is to use both batts for the start, then run 'em separated on 2 busses. But it's experimental.
 
Henning said:
Batteries are pilot replaceable.
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...as long as the batteries are identical or on the TC with no W&B change.

I ran into this when removing a Gill and installing a Concorde. A&P said good to go and I mumbled something about paperwork...A&P proceeded to supply paperwork (Concorde came with STC) including new W&B.
 
MAKG1 said:
I've been known to get 5-6 years. Not having freezing weather helps. I don't buy premium anything for 1/4 million mile vehicles.
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I had a customer come in yesterday to talk to me about replacing his battery in his truck. He wanted me to know that it was the ORIGINAL battery from September 2002!!! :yes: I told him we needed to charge him double, since he skipped 2 replacements!! :D
 
PPC1052 said:
Yep. You are supposed to make a log entry though.
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Which is that much easier when the Gill company attaches a self-adhesive sticker with the battery brand, model and serial # for you to simply "slap" in your logbook. Love it!

FWIW, batteries are like any other devices. Poor quality means shorter life. Mistreatment means shorter life. Neglect means shorter life.

Also, as pointed out earlier, depends on what devices were turned on. For example the DME and xpdr would be on the same avionics switch. Beacon, pitot heat etc would have separate switches but the last renter might have left them on.

I would report the weak battery to the owner so that they are not surprised when it dies completely.
 
It sounds like the OP's battery is quite weak. A good battery will last a fairly long time without having the engine running. I've lost an alternator in flight a few times, I've never had a problem having the battery hold enough of a charge to start the engine a few times, run the radios, and run the electric landing gear.
 
The summer heat in AZ is a battery killer, especially if it sits at all. If it's a rental that flies almost every day that will be better, but even so the climate here just isn't good for batteries. It's probably just near the end of its life.
 
Knock on weed, but... my airplane battery has been strong like bull for a couple years now. I have never kept it on a trickle charger or anything and it (along with my SkyTech starter) has always managed to crank pretty well even after having the avionics on for a while.

This will be this battery's third Denver winter so it'll be a test.
 
petrolero said:
Knock on weed, but... my airplane battery has been strong like bull for a couple years now. I have never kept it on a trickle charger or anything and it (along with my SkyTech starter) has always managed to crank pretty well even after having the avionics on for a while.

This will be this battery's third Denver winter so it'll be a test.
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Aren't you freezing your Arse off right now in Denver? :yikes: I hope your airplane is in a Heated Hanger.
 
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