Oooh... 6 feet of LEDS, looks like those addressable LED strips, that's going to be a lot of power, probably several AMPS.
A small battery simply won't give out that amount of current and, if it did, the 5v regulator on the Arduino board would go POOF almost immediately.
By far the simplest solution would be a 5v plugtop power supply which can supply enough current for your LED strip - you'll have to check how much current the strip you have will need.
You'll also need some thick cable to wire from the power supply to your Arduino and strip, powering the Arduino 5v and the LED 5v from that.
If you really want a battery, it would have to be a big one like: 12v-7ah-BATTERY which you can wire to Arduino Vin and you'll need a 12v to 5v converter (again, to supply several amps) to power the LEDS.