electrical newbee here please help

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I just bought a little 5 w solar panel and as I took out of the box I tested it with an voltmeter. I was getting -ve 20 V in bright sun light. Is this wired backwards? It is after all made in china. The red terminal that comes out of the solar panel clips to the +ve terminal of the battery the book says. But like I said when I tested it, that was actually the -ve terminal .I am afraid to hook it up to the battery, I am pretty sure I can damage it with that little 5w if I hook it up the wrong way. Thank you in advance for all your help........Constantin