Sloep mode - turn it into a dumbphone rescue sloep

What would be the use? I think most people are perfectly aware that using a mediaplayer or browsing the web requires a significant amount of battery. Need the endurance? Don't run the apps. No need to actively block them. I would however welcome a powersave mode, like the N9, in which things as background connections are disabled, screen brightness is lowered, etc.

A visual cue signaling that high-energy apps are running might be a nice touch. I wrote a small python script for the N9 which used the notification led to indicate the current CPU-load, which correlates quite nicely with energy consumption. Of course using the battery load would be better. You get the idea :)

Use? If it is such a bad idea why is HTC driving their marketing campaign with such a "low power" feature? The use is for average Joe (and they are not aware! non of them!), having a button "fire and forget" and be sure that it will last the next 48h - and not a "come on what will one browser page cost me, go away notification devil I want that page loaded" - also you can manage power more efficiently if you know you won't need specific hardware in that state. So if it is possible and effective dead- instead of sleep-states come to play. powersave-mode like on N9 would be something in between, for me this is my usual behaviour - I turn off background connections when I am not at home... I could make use of profilematic too... but this is about the lowest consumption possible while maintaining call/text features only.

So... the use would be primarily for marketing? I'm very skeptical about the real benefit in terms of extra power saving of this feature over the power saving mode like N9, and stuff already in Sailfish. I don't think there will be much more to gain; much of the hardware isn't active anyway when idle, and with background connections disabled there will be no syncing.

Even then, now I get 2-3 days of use, with 3G, WLAN, BT, internet, syncing enabled and a few browsing sessions.

That is why I tagged it skunkworks - I do not know if it is possible and currently do not have time at hand to test what I may deactivate my own (without causing reboots) to measure long-term consumption impacts. I tweaked my netbook for lowest possible consumption, it is specified with just about 6h on average use (9h idle and 4h on load). Under windows, lowest consumption was 8.8W idle, I got it down to 7.5-8W under linux. That is >10%. I get 5days out of my jolla, so when you are on the last day how about reducing the average consumption by 50% so you get another day? When your phone turns into a dumbphone, you will use it like one - main impact is the display stays off for a longer time. Then the sync-watchdog is not needed so the device is not awakened every 30min/hour to check for tasks. This list can get pretty long when you are looking for it. Powersave mode is not aggressive enough. Sure it can be used for marketing. (I get ~5 days by behaving like powersaver, can get 7!)