That's not unusual. When phones charge Li-Ion batteries, they don't keep them at 100% as that would be very bad for the battery. They take them to 100% and stop charging, allowing the battery to go back down to about 90%, then start charging again. This cycle continues until you take the phone off the charger. However, to keep the consumer from thinking something is broken, the phone will initially report the battery at 100%. So depending on where you are in the cycle when you take the phone off the charger, you'll drop a bunch in the first few minutes.
There is such a thing as "bump charging" to get all the way back to 100%, but it's not good for the battery. And since the battery in the DNA is not removable (and therefore not replaceable), doing anything that's bad for the battery seems really dumb... which is why I also recommend against wireless charging (creates heat, which is terrible for the battery).