Hey guys, I am the market for an external battery that I can leave in my car and use it when I need it. I don't want to pay a whole lot of money. I just need something that I can charge leave in my car and when I come into a situation where my phone is going to die and I need to use the GPS or make a phone call I can just plug it in and be good. I found a few on Amazon, but I showed lights that indicated that it was fully charge. My concern with those is that they won't hold a charge an extended amount of time. I need one that I can keep charge and not worry about it running out of juice within a few months of not using it. Any suggestions? PS: My cig lighter doesn't work.