Soldering iron that plugs into car lighter socket. Have some electrical work to do on my car, and no garage. 
You could get a gas powered one. That’s what I use for those situations.
I have a gas powered one that comes with a few other tips. It’s is one of my favourite tools - the Pocket Blow Torch.
Great for caramelizing Creme Brulee’ too.
I had a gas one years ago, when it worked it always ran too hot for the small tips. After a few months in storage it was fubar, never worked again.