Utter rubbish. Does not protect against backflow of voltage. Keeps at no use of mobile phones grade probes battery level. I had it be this summer in the blazing midday sun until the evening dusk. Then, as the sun vanished, the residual stress is sucked out of my cell phone battery - Conclusion: battery broken. Easy Return of goods thanks to Amazon Customer Service. But sellers sitting in China, ie no compensation for my smartphone! Can stay away !!!!!!!!