I have a SoundLogic solar-powered power bank which has a 5v @ 1A/2.1A MAX output, is it safe to use it with my pi 3? Im kinda worried about using it and it frying or breaking when the battery energy goes down.
I have powered a Pi Zero from a power bank and when the power ran out the power bank cleanly cut power, no brownout. I would assume you will get the same behaviour and therefore not be a frying problem.
However, just cutting the power from any Pi is not recommended. If the Pi is writing to the SD card when the power goes down you could get corruption which proves fatal.
If you can run the SD card read only, then you should be safe. Try googling "pi sd card read only" - eg Charles Hallard has a good tutorial for this. The only thing I would add is to use a USB stick to keep any logs etc on and if that becomes corrupt then the Pi can keep working.
I did this years ago with a Compact Flash card in an old PC running Slackware, so I know its possible, I've just never tried it with a Pi.