Flying after more than 24 hours since battery was charged

[skyeboysteve]

I'm planning a 4 day hike in a couple months to a remote lake at the base of an active volcano, which requires two days of hiking from the nearest probable charging point. Bringing a small generator along on a challenging (at least for me) hike isn't going to be too feasible--so my question is how important is the general recommendation of never flying after 24 hours since your battery was last charged?

I'm a little confused as to when batteries start auto-discharging, but assumed it was 24 hours after charging, and the time period specified (number of days) in the Go App dictated how slowly it would discharge. I've seen other points of view stating that the battery doesn't discharge till AFTER the number of days specified in the Go App has occurred.

In any case, the collective wisdom seems to be, don't fly with a battery that hasn't been topped-off in the previous 24 hours.

That being said, is there any known leeway or precautions one can take if a battery is two or three days "old" from its previous charge?--like for example not flying to less than 50% INDICATED levels? Or is it simply that batteries that are more than a day old just act unpredictably in general?

Thanks to anyone who can help me figure this out.

 

[chrismartin3391]

I personally didn't hear or know of the 24 hour rule and have flown pretty much every time with charges done over a 24 hour timeframe and have had 0 issues. I just check the level before flight. Get four green lights and go.

 

[skyeboysteve]

I personally didn't hear or know of the 24 hour rule and have flown pretty much every time with charges done over a 24 hour timeframe and have had 0 issues. I just check the level before flight. Get four green lights and go.

Interesting. I've just read that sometimes battery voltages are actually lower than indicated, and that under load one's battery can fail due to the voltage drop during high amp operations that can exceed the low voltage safety switch that turns the battery off (ostensibly to save the life of the battery); which of course is illogical when that same battery is floating 400 feet above the ground.

How many days have you gone since your previous charge, and what do you have your discharge number of days set at?

 

[53-63-6f-74-74]

The batteries have their own software. You can set the 'discharge' time up to 10 days in the DJI app. I've never heard of any 24 hour rule and I personally wouldn't worry about it at all. If I had the discharge setting at 3 days then I might be more concerned.

 

[skyeboysteve]

Here's an example of what I saw posted in the DJI forum. DJI smart battery tips and usage

Granted perhaps this only pertains to cold weather flying?

 

[chrismartin3391]

Interesting. I've just read that sometimes battery voltages are actually lower than indicated, and that under load one's battery can fail due to the voltage drop during high amp operations that can exceed the low voltage safety switch that turns the battery off (ostensibly to save the life of the battery); which of course is illogical when that same battery is floating 400 feet above the ground.

How many days have you gone since your previous charge, and what do you have your discharge number of days set at?

Mine is set at two or three. Odd though my batteries are always full after a week or so or maybe at 90-95%. I was going to post on here and ask if that was normal.

 

[alokbhargava]

I usually top off the batteries to 100% on the day of flying.

You should start flying with full voltage. The reason for that is the mapping the battery discharge characteristics into the aircrafts calculations. More deviation from 100% at starting will create more inaccuracies in the computations. In reality nothing bad happens if you start flying with say 95% charge as when you reach the critical calculated voltage of say 10%, actual battery voltage may be around the same voltage. Lower the starting voltage, higher the risk of actual voltage at critical values and there are chances that aircraft suddenly drops to ground because of lack of charge though calculations still shoos enough juice.

In short if you start at 95%. Increase the critical voltage setting to avoid mishap. But if you have time and source of charge, it is advisable to fly with 100% charge to match calculated values with the actual values.

 

[sar104]

I'm planning a 4 day hike in a couple months to a remote lake at the base of an active volcano, which requires two days of hiking from the nearest probable charging point. Bringing a small generator along on a challenging (at least for me) hike isn't going to be too feasible--so my question is how important is the general recommendation of never flying after 24 hours since your battery was last charged?

I'm a little confused as to when batteries start auto-discharging, but assumed it was 24 hours after charging, and the time period specified (number of days) in the Go App dictated how slowly it would discharge. I've seen other points of view stating that the battery doesn't discharge till AFTER the number of days specified in the Go App has occurred.

In any case, the collective wisdom seems to be, don't fly with a battery that hasn't been topped-off in the previous 24 hours.

That being said, is there any known leeway or precautions one can take if a battery is two or three days "old" from its previous charge?--like for example not flying to less than 50% INDICATED levels? Or is it simply that batteries that are more than a day old just act unpredictably in general?

Thanks to anyone who can help me figure this out.

You might get a few extra seconds of flight from a newly charged or topped-off battery, but the difference should be minimal in the period before the battery starts its self-discharge process.

And, just to be clear, the self-discharge setting specifies the time before the battery starts self-discharge, not the duration of the self-discharge process. Self-discharge is a rather slow process, necessarily, since conservation of energy dictates that the entire stored energy must be dissipated as heat in a resistor inside the battery circuitry, which then has to escape by thermal transport (conduction and convection) from the battery.

As an illustration of the energy involved, for a 5.350 Ahr, 15.2 V battery weighing 460 g (P4), if that heat did not escape then the battery temperture would theoretically increase by around 750°C (Cp is approximately 850 J/kg/K) . Of course it would combust well before that temperature rise was achieved.