Can I get help with battery math...batteries-inverter-coffee

I also carry a mini Keurig with me, we quite often don't have power so I found the below press that can use Keurig cartridges, or it can be used as a regular press. I like using the cartridges as it's no mess and easy clean up when we may not have copious amounts of water to rinse off coffee grounds.

http://www.amazon.com/Cafejo-French-Press-Adaptors-Various-Samples/dp/B00800525U/ref=sr_1_1?ie=UTF8&qid=1455741787&sr=8-1&keywords=cafejo