My grandmother once noted 'Rick, if there's a lemon in the bunch you'll get it!' and unfortunately she's been proven right more than once in my life.  So it went with this inverter...the first one that came had defective wiring inside and eventually after blowing several fuses burned completely up and I wrote a scathing review before tossing it in the trash.  But I am nothing if not fair minded and have long ago learned that most often the second time's the charm for me so after being contacted by the manufacturer and offered another one to try I said, 'why not'.It arrived this last Friday as we were preparing to go for a camping trip and I thought that would be a perfect testing ground.  After gingerly plugging it into the cigarette lighter that it's predecessor has so disliked I was surprised to see the blue light come on that indicated it was powered and ready to go.  My cell was pretty near dead so I charged it on the way up to the mountains and over the course of the weekend we used it to charge a laptop (and there are three pronged outlets on it (2) that make it convenient to use a laptop charger along with usb plugs for the cell phones.  The real test was Sunday when we took it and attached the battery cable hookups directly to the truck battery to run a drill to drill two nail holes in a board to put up a feeder and it worked like a champ.I can vouch that it has excellent safety circuits since the first one kept blowing fuses instead of burning up my cigarette lighter circuit and only finally shorted out when I attached it directly to the battery.  So I am actually very happy to recommend this product because the first unit I got proved it won't hurt your vehicle if it overloads or does have a manufacturing problem and I can personally attest to the fact that the manufacturer stands behind it big time.I'm changing my rating to 5 Stars because it did everything we needed of it on the camping trip and is well built.But note that the fuse in the lighter plug in is 10amp and should be replaced with a 10 amp should you ever need to.  Which seems unlikely after it worked all weekend with no issues. The book refers to a 35amp fuse but that's inside the unit itself and is not the one in the cigarette plug.  And make sure you read the book thoroughly so you know how to set it up for direct connection to a battery before you do so.  Hard to find a 500amp inverter so I'm glad to get a chance to praise it after all.  I recommend this excellent product with no reservations.