I have to verify when I get home, but I've probably found the problem... Seems as a stupid copy/paste problem. No call to analogreference(INTERNAL). Don't know how I've been able to overlook this for a week now, but... Will check back with result later on...
@sundberg84 - Indeed missing analogreference. All good now, even got a battery value of 102 % 
@sundberg84 - Indeed missing analogreference. All good now, even got a battery value of 102 %
I have to verify when I get home, but I've probably found the problem... Seems as a stupid copy/paste problem. No call to analogreference(INTERNAL). Don't know how I've been able to overlook this for a week now, but... Will check back with result later on...
@sundberg84 - the only weird part is that analogread() returns a value of 300, which in turn is below VMIN; and hence a negative value (1,04-1,9)/(3,0-1,9) = -78%.
But if I understand you correctly the next two steps in the troubleshooting process would be;
Thanks again 
@sundberg84
Hi,
What I've done is this;
Measured voltage on PWR/GND which returns 3,2 V. I've measured voltage on GND/Vout on the battery booster which returns 3,36V. However, analogread always returns something like 300 +/-10, which (using the formula provided) indicates a voltage of 1,04 V and a battery percentage of ~30%. This has been the case with brand new batteries as well as old ones...
Hi,
First of all, thank you @sundberg84 for this great PCB. Super easy to work with. Still; there is one question that I haven't been able to figure out yet.
I'm running my pcb as a battery node and want to monitor the battery status. However A0 always returns a value somewhere around 30 +/- 15 - even with brand new batteries. Calculated into voltage, this would mean around 1,04V.
I've checked and double checked that I'm using 470k and 1M resistors.
I've also measured using a multi meter, with incoming value of 3,2 V and outgoing from booster 3,36V.
Any ideas that might point me in the right direction for solving this noob issue?