Can I connect a Dell XPS 18 battery from the outside?

I need to use my machine as a mobile device, so I need a power bank. I think the most efficient way to do this would be to connect, say, four XPS 18 batteries in parallel, and then to connect them to the motherboard. Can I use the charging contacts at the bottom of the device, or maybe attach a cable to the battery inside in parallel, with a lead running to the outside of the housing, for connecting the external batteries?

It seems that using just XPS 18 batteries instead of a power bank would be more energy efficient, possibly with no need to convert the voltage, with less added weight.