Also need to attach a battery pack

See several examples in here but is there a module that adds a battery to it or do you have to buy it as a kit with the batter pack?

What imp do you have - the april breakout board will work fine with either a 9v or a 6v (4xAA) pack soldered to the “P+/P-” pads on the board.

You can attach a rechargeable pack too, but there’s no on-board charger.

April Rev 3

Very very easy option: buy a USB battery pack.
Next easiest option: 9v battery or 4xAA battery.

The April has those pads just behind the USB connector.

Can you point me at the amazon usb battery pack?

…there are literally thousands. Anker stuff is generally good. An imp in powersave mode takes around 10mA, so a $10 3350mAh powerpack, in a perfect world, would run an imp for almost 2 weeks without it even needing to go to sleep.

In real life most of these powerpacks aren’t terribly efficient and not great with low drain devices (they’re usually used to do 1A+ charging to phones in short bursts). Your mileage will vary.