Mobile power supply for stand-alone Arduino
Once development is finished you might want to operate your stand-alone Arduino with batteries.
So you get yourself a battery holder and a clip to connect it to your board.
Most of the battery holders take 2, 4, or 6 of the AA cells, each giving 1.5 volts.
But Atmel specifications tell us the ATmega328P wants 1.8 to 5.5 volts, and 4 batteries give about 6 volts.
A short test showed the chip did not get damaged, but it did not work properly with 6 volts.
So, 3 batteries would be nice. But how to manage?
Just take a square wooden bar (or a round one), not wider than 0.5 inch (14 mm), cut it to 1.9 inch (50 mm) and take a thin wire to connect top and bottom.
(If you got a bar of aluminium, you don't need the wire, of course.)
And insert that wodden battery in the battery holder.
If you are using rechargable batteries which give 1.2 volts you can use four of them.