That Bangalore Broadside Models B and C are powered by a mini internal battery.
The Bangalore Broadside Model C (with the solar panel) uses its solar panel to keep the battery charged up during daylight hours.
The Model B (with no solar panel) needs to have its battery removed and charged up manually at regular intervals.
If you have a Model C, note that the solar panel must have line-of-sight to the sun to charge up. Make sure it's not hidden under hedges or trees.
The Model B's battery can be charged up by removing it and plugging it into a Mini Battery Charger.
You can check the amount of charge left in your battery at any time - see this FAQ for more info.