How to power Arduino externally for long term? For a robotic project, I need to keep an Arduino powered up for a long time in an outdoor environment. What can I use to power the board?
If battery is the only solution, can the device tell me remotely that battery is getting low?

It needs to be powered for at least few days ( at least). The unit monitors an outdoor sensor that is shaded from sun but still exposed to wind and moisture. The unit does not move.
There are several options for Arduino power in an external environment.


Wall wart: Connects to a wall socket, provides a great long-term source of power
Rechargeable battery: Doesn't last long, but they can be recharged and monitored with a low cost board
Alkaline Battery: Last longer, there are some monitoring systems available.
Solar: Only works when the sun is out, unless you combine it with a rechargable battery (example)
Nuclear power: NOT RECOMMENDED!!!