For solar Bh when the solar power is not strong enough during cloudy day the Amp intelligent switches to Dc. During Strong solar power the Dc Battery is automatically charge.
Even for area that has frequent electricity interruption the Bh still have sound and birds won't run away. The battery works as a standby generator.
In other words whatever situation the Bh still have sound. High power output can operate up to 60 or more piezo tweeters. 
As indicated above it switches power supply automatically. Even when there is power interruption the Bh still have sound.
This is a chargeable battery , very small in size and can be constantly connected to the Amp.Best of all it is Cheap! The Battery can last 20 hr.Amp and battery sold seperately.
For price call 012-3173811