As much as I love this thing, I wish it only came with a 9V battery connector. This device connects to a micro USB charger to charge the internal battery. I'm sure this is a one-time issue in my case, but on a full overnight charge the battery lasts me about 4 hours even when it's turned off. I have to use it on the charger most of the time, which is a nuisance given all the cables cluttering up my desktop. Update: I finally took it apart (4 screws that fell out) and found a very bloated battery, which is not the tester's fault. The battery has a small circuit that prevents rapid discharge and overcharging. Looks pretty high quality, I only got one of poor quality. The cool thing is that I found the exact same battery on Amazon - same circuit, same voltage, same mAh and same connector!