No..Its not quite that simple.... - Yes! - a discharged battery, is a discharged battery. However its different from what angle you look at it...
Because....
There can be a HUGE difference between the True capacity a discharged battery is holding, and what the smart circuitry in the battery/aircraft "Thinks" its holding and reporting as a percentage.
This actually means that the aircraft may Think and Report a different percentage capacity from the True Chemical Charge State of the battery, because the reported state is a calculated value over time.
Let me explain with an example:
- When a battery is charged, the Smart circuitry in the battery keeps measuring the power (Current, Voltage over Time) going into the battery (mAh). Once the LiOn battery reaches its maximum allowable safe Voltage (normally 4.2V) the smart circuitry memorises the charge (as 100%) gone in and disconnects the charger. At this point your Phantom battery is fully charged and a normal battery reports 100%
- When a Battery is Used (put into the Quad and switched on) the Smart Circuitry starts to measure the Power being withdrawn from the battery.... This is where the calculation comes in... The smart circuitry calculates what’s Gone In minus what’s come out then applies a manufacturer’s efficiency formula/algorithm and reports the remaining battery Capacity in %
Now.. The Calcualtion and/or Manufacturers Efficiency formula, although quite accurate, does not always work the same for every cell in the pack as every cell is chemically slightly different. So as time goes on and the battery goes through a number of normal charge & discharge cycles the Calculated Value may differ from the True Chemical Charge a battery holds. – Also partial discharge/Charge cycles and Cold temperatures play havoc as they change the chemical chracteristics and deviate from the expected calculations and value at either end (Fully Discharged or Charged)
What’s even worse is that over time, on a stored battery, there is Safety Storage Discharge (after a set number of days), some internal self-discharge (not too bad in Lipos) or the smart circuit itself may draw out a very small amount, but over a longer storage period it all adds up, such that (And this is the IMPORTANT Bit) the Memorised/Calculated state of a battery may differ greatly from the Actual/True chemical state. Hence Your Battery Is Out Of Sync and is reporting a wrong capacity percentage. i.e. Go App may be reporting 60%, on a partially charged pack, whilst the true charge (Chemically) may be only 20% - hence when you fly and apply full throttle, there is a big drain, the voltage suddenly drops Critically low and your Phantom falls out of the sky.
So an inexperienced Pilot is let wondering why his craft ran out of power so quickly - Thats why we say - Try Not to fly on a partially charged pack/stored pack.
This is why we have to cycle packs – To Reset the Calculated Value that the Smart Circuitry in the battery is reporting and to bring it as close as possible to the Chemical Charge State of the battery. (Note: Not to extend the life expectancy of the pack) – This reset by the smart circuitry happens over a defined set of values. i.e. when the % capacity falls below 10% or the voltage falls under a certain value (I think 3.2V at rest). The smart circiutry then memorises that as the low capacity, as close as possible to the True Chemical state and as you then charge the pack fully, it memorises the maximum capacity as 100%..... Now its once agin in Sync..., and then the calculation starts again as you use the pack... so on..and on...
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