Evan Rodgers at The Verge has come up with a DIY solution for those looking to create an external battery for their MacBook notebooks on the cheap. Granted one could always go out and purchase external batteries but that will easily set you back a couple of hundred, so for those looking for a DIY project and have the tools and a bit of the know-how, perhaps this is a project you might be interested in embarking on.
According to his instructions, you would require 2x 12v CCTV batteries, a 3rd party MacBook car charger, soldering iron, flux, solder, heat shrink tubing and 5x blocking diode. These items are readily available at computer shops and hardware stores so getting access to them shouldn’t be a problem. The rest of the instructions are available at the source link below, along with a video where he goes on to further explain what else you need to do. Not just limited to MacBook computers, it seems that this DIY external battery should also be compatible with any device that has a car charger as one of its accessories.