D'Addario PW-CT-26 Nexus 360 Rechargable Tuner 

D’Addario’s rechargeable Nexxus 360™ Tuner offers fast, accurate tuning without the cost and hassle of replacing batteries. The discreet, clip-on design features 360-degree rotation, plus a super bright, full color LED display, assuring a perfect viewing angle and screen clarity in any lighting. Simply plug the supplied USB cable into any USB power device as needed and enjoy 24 hours of tuning time per charge.