iPad 2 Battery Drained Plugged In

[hansololo]

i have my ipad2 hooked up to speakers playing spotify in the office as it's plugged into the wall. by mid day the ipad dies. i'm not running any other apps in background, location service is off, notifications are off, only things running are spotify and wifi. any suggestions to keep the ipad from dying? it's weird to me that it would die on a charge.