Re: NFC tag emulator
I guess it depends on the phone but with my Nexus 5X it easily reads my tag with all the 3 batteries removed. I guess it also depends on which part of the phone you use depending on where the NFC-antenna is located on the phone.
If I where you I would closely examine the areas where you soldered. Maybe there some tiny bit of solder shorting something out.
Also from the FAQ:
Q: How long do the batteries last?
A: Because of the automatic power-saving feature, the battery current consumption when no reader field is present is more than 1000 times smaller than when the field is present. Because of that, the battery life strongly depends on the frequency of use and duration of interaction with PCD. Typical capacity of AG8 batteries is 45 mAh, while the active current consumption of the reader with full batteries is around 6 mA, resulting in at least 8 hours of continuous work in reader field. If the field is never applied, it would *theoretically* take more than 20 years to drain full batteries.
Basically what is says is that the chip is only fully powered when a field is present, without a field it goes into powersaving mode. I suppose the chip has two separate power feeds. One that just keeps the data intact and one (that is enabled by the field) that powers up the chip. For you only one feed works and not the powersaving one.
EDIT: No, only one power feed to the chip. But it can be put into power-down mode and be woken up by external interrupts. I measured the voltage between the ground and the +3.3-5.5V pin/hole and for me it's 3.52V with batteries right now and when in NFC field it raised to 3.7V. I guess it should be higher but I think my batteries are about to run out. Did a massive 8-9 hour print the other day.
EDIT2: Whats your voltage between the pins? With fresh batteries I suppose it should be around 4.6V.