This article is about how the capacity of the Lithium Polymer (LiPo) batteries used in the Bluefly degrades over time or by other mechanisms. It should be read in conjunction with this article that describes how much power the Bluefly consumes.
In normal operation the Bluefly should charge to 4.2V in about three hours (and the red light should go out). When the voltage falls below 3.6V the Bluefly shuts down and should be recharged soon. When it is shut down the Bluefly will still consume a very small amount of power, but a fully charged fresh battery should last for at least a few years in this state.
When a LiPo battery is new from the factory it should:
- Have around the factory stated capacity in mAh, although manufacturing inconsistencies mean that this rarely exactly accurate.
- Provide a stable voltage when the Bluefly is consuming power.
- Be 100% charged at around 4.2V, and at about 10% charge at 3.6V.
When a battery performance degrades each of these things can be affected:
- The capacity in mAh can reduce, slowly at first, then when it is old enough will degrade quickly.
- At peak, the Bluefly might consume just over100mA with bluetooth and GPS and sink alarm sounding. If the battery has degraded (and the internal resistance has increased) then the voltage might drop markedly when there is peak power consumption, perhaps even enough for the voltage to drop below 3.6V and the Bluefly to shutdown.
- Charging an old battery may not be able to get to 4.2V no matter how long it is connected to the charger.
The main things that affect battery degradation include:
- The age of the battery. There is nothing you can do about this. After a number of years a battery will just perform worse.
- Heat and Cold. If a battery is warm to the touch, or below freezing, and it is charged or used, the battery will degrade quicker.
- Hi or low voltage. A battery stored at full charge or at very low charge for extended periods will degrade quicker.
If you notice that your Bluefly does not last as long as it used to, or it shuts down from low voltage in flight (particularly when its cold), it might be time for a new battery. It is ok to operate the Bluefly connected to an external charger, but a semi working battery also needs to be present.
If you plan to store your Bluefly without using it for many months then it is recommended to charging to about 80% capacity (around 4.0V), then shutting it down. If you are going to store it for years charge it to the same amount then disconnect the battery.