To add shortly to this, we had issues with the standby battery on our C172S (aeroclub). It didn’t last the 10 seconds and IIRC the battery was exchanged.
Sorry I had not seen that thread earlier.
It seems to me that the OP has not kept his POH up to date.
Present version is rev. 2 (2010)
The only significant amendment I could find is that the 20 second test is now a 10 second test only.
So your battery is (was) ok.
The same way mail batteries can be desulfated and maintened thanks to specific chargers, can the G1000 standby battery used on Cessna set up benefit from such treatment ?
It is a lead sealed battery, but from what I know it has a specific connector…
There is test in the Cessna maintenance manual, I can’t remember the interval, but it’s a full capacity check. I would recommend to do that, as that would give a good idea if you have an indication problem, charging problem or that the battery is in poor condition.
Thanks! A 50 hr service is due shortly, and I’ll ask for a check of the standby battery.
@Airborne Again
There is test in the Cessna maintenance manual, I can’t remember the interval, but it’s a full capacity check. I would recommend to do that, as that would give a good idea if you have an indication problem, charging problem or that the battery is in poor condition.
I have replaced the batteries a couple of times, they last only a few years.
All batteries perform significantly worse in low ambient temperatures.
Agreed. But still…
It sounds like the standby battery is shot.
Let me rephrase my statement. I believe the battery is showing signs of weakness that indicate that it will soon become totally unusable.
In October 2013 I reported to the owner of the DA40 I am renting that I thought that the main battery was reaching its end of life. The starter motor was cranking the engine slower than usual. I sometimes barely could start the engine for the first time in the morning, but after having run and charged the battery, it seemed to behave normally. The amps load on the alternator stayed high longer than usual, and was higher than usual.
I heard from the handling agent that they had assisted pilots in jump starting the engine from external power (which is btw something that I would avoid). One morning I was scheduled to fly with the owner, we barely managed to start it, taxied to the fuel pump, and after refueling we actually did not get the engine started.
The owner was reluctant to change the battery (about 600 € IIRC) and looked for all sorts of explanations as to its condition. We went to several mechanics and avionics shops before he was convinced that there was only one solution: change the battery. But it took close to 6 months of increasing pains until it was done…
Check the battery, and replace it.
I wouldn’t be too worried. All batteries perform significantly worse in low ambient temperatures. Especially so after the aircraft didn’t fly for some time. So, you really caught it it’s worst moment. No wonder it flunks the test.
So if I understood correctly this standby battery powers the essential bus. If the main battery dies, and you loose your alternator, only the essential bus is powered by the standby battery. The PFD is powered by the essbus, and so are essential nav/com equipment. I suppose that AHRS and air data are also powered by the essential bus.
It sounds like the standby battery is shot. If it is a lead acid battery, ans you can open the cells, you can measure the weight of the acid in each cell. Chances are that you will find one or two cells that are low on juice.
Yes, but the G1000 is supposed to display bus voltages, I think
This test is done before the electrical system (and thus the G1000) is turned on. The POH advises that the test should not be done with the G1000 in operation.
Yes if it’s really the battery and not the voltage warning light.
It is not a voltage warning light. It is a special indicator light used only for the load testing of the standby battery.
The standby battery has an TEST/OFF/ARM switch. In the TEST position it is connected to the test load and to the indicator light. In the ARM position it is connected directly to the essential bus. The essential bus is also powered via diodes from both main electrical buses, so as long as one main bus provides power, the standby battery is charged. If none of them do, then the standby battery powers the essential bus.
I understand but I mean that aren’t you at some risk of reducing its life by adding more discharge cycles?
That shouldn’t actually be a deep discharge cycle.
The POH doesn’t say.
Yes, but the G1000 is supposed to display bus voltages, I think
My experience with batteries that start acting up like that is that they’re toast and you’d should replace them the sooner the better.
Yes if it’s really the battery and not the voltage warning light.
I dimly remember that last time I flew the 172SP G1000, that particular warning light looked quite flaky.
