Interesting hint, I'll give it a try. Still not the solution I was looking for, but maybe good enought to see if this is working as expected, still a dirty hack. For thoose who interested:

I have a script in /home/nemo/scripts/battery-drain-notify.sh:

#!/bin/bash
DIFF=5 #difference in battery capacity to care about for 15min - I have to test this value
NEW_CAP=$(cat /sys/class/power_supply/battery/capacity)
OLD_CAP=$(cat /tmp/batt-old)
if [ $(($OLD_CAP - $NEW_CAP)) -ge $DIFF ]
    then
        notificationtool -o add -A Battery-notify -c x-nemo.battery.lowbattery "Battery drain exceeded" "Battery drained in the last 15 minutes more than $DIFF%"
    #else
        #notificationtool -o add -A Battery-notify -c x-nemo.battery.removecharger "Battery notify status" "Everything is fine and running :)"
fi
echo $NEW_CAP > /tmp/batt-old

And since I have no cron is installed, I used timedclient-qt5 to run this script every 15minutes, as one-time-command this should also survive a reboot (I'm not sure how to use timedclient-q5):

timedclient-qt5 -a'whenDue;runCommand=/home/nemo/scripts/battery-drain-notify.sh@nemo' -r'hour=00;hour=01;hour=02;hour=03;hour=04;hour=05;hour=06;hour=07;hour=08;hour=09;hour=10;hour=11;hour=12;hour=13;hour=14;hour=15;hour=16;hour=17;hour=18;hour=19;hour=20;hour=21;hour=22;hour=23;minute=0;minute=15;minute=30;minute=45;everyDayOfWeek;everyDayOfMonth;everyMonth' -e'APPLICATION=batterynotify;TITLE=test'

Thanks for reading my question but this does not satify me. I don't want to get notyfied if it is to late, the 10% warning is totally fine (in my opinion). I use "Battery Log" to get the estimated runtime and this is fine too. A notification at a minimum remaining runtime would be better, but still useless.

I want the phone to keep my remaining runtime as expected (thats not right and not poossible due to user interaction but this give an idea of what I mean), it can detect if something happens what should'nt happen.

The last time this happend I thought about powertop too (good hint, I just installed it). But this is not the point, the missing automatically thing bothers me.

Most time aliendalvik is off, but sometimes I forget it. One time it was the browsers fault, or mine .. I left a website open with a running script refreshing the site, so it's not always android :).