Left the unit last night fully charged at 100% and switched off wifi and bluetooth. This morning it was already down to 87%. Pretty hungry for a standby.
On another more interesting note: I was playing a bit yesterday with the filters. They have somewhat confusing names, since Sharp and Brickwall are often interchangeable, and Minimum phase and Apodizing as well. Plus an unknown Hybrid filter, which I googled and couldn't find anything about. Incidentally new FiiO X7II uses the same filter names, so it must be some Sabre house terminology. X7II uses ES9028Pro chip as opposed to AP200's double ES9118C chips, but the filter names are identical.
Russian headfier romanrex has a highly informative website with measures and specs of different dacs, amps and headphones. He covered recently all the filters of X7II. Since they are identical with the AP200, I though it might be useful for AP200 owners as well, to compare the impulse behavior of different filter settings:
http://reference-audio-analyzer.pro/en/report/dac/fiio-x7-2-apodising-fast.php