After a number of days of non use ( ten, I think) , a fully charged
battery will start to discharge as the
batteries don't like to be fully charged for a long period of time. That's the intelligent part.
If you tap the
battery to check the charge, it will reset the timer and maintain the current charge level for another few days before it will start discharging again.
If you don't keep an eye on the
battery level while it's not being used, it WILL discharge down to zero and you'll have a brick for a
battery.
There's a hidden 10% of power in the
battery to maintain the intelligence, but once that is depleted, so is the
battery.
It's best to set an appointment in your phone calendar a couple of times per month to check the
batteries and charge up to about 75% (3 LED's ON, 4th blinking) if you're not going to be flying for a while. Check the remote too.
Here's a video about the care and maintenance of the
Spark batteries.
It's long and informative, but if you have the time, pop some popcorn and enjoy.