My friend has a beautiful P22 . At band practice last night, she had the guitar in "electric" mode and it sounded great for about 9 songs. We than went to practice a song which required her to play with the piezo and absolutely no sound. Please tell me that this is just a battery problem. Unfortunately last night, none of us had any spare 9V batteries with us, so we were not able to determine if in fact the problem is related to a dead battery. We checked all obvious things like the amp, cables, PA etc. Any thoughts as to the cause of the problem? Hope fully just needs a battery change???