re: Edward Snowden designs phone case that shows if data is being monitored

If there's another battery (or a supercapacitor), it's possible to remove the first battery, but then the question becomes "with two batteries, can they be hot-swapped?", which is quite a different question. So - no, without a source of power, it is not possible to draw power necessary for functioning, certainly not longer than a few seconds. Now, the real question appears to be "is it possible to hide another battery inside the device?