Electron & UltraFire battery


I’m new of this community and I am looking for some good advice.
I’m working on a project for a compact meteo/wind station and after few successful weeks of testing I’m now at the conclusion that I need to change the battery coz 2000mAh is not enought.

A little step back.

Actually I have the standard LiPo batter and a small solar panel (200mAh) directly connected to GND and VIN, it works well and I can recharge what I lost during night in a couple of hours of sun but based on my tests with this configuration it can survive 2-3 days of bad weather.

So, what about move to a UltraFire MRK26650 battery rated 7200mAh 3.7V ?
The one I have is protected from short circuit, over charge and discharge.

Can I remove the original battery and connect the UltraFire to the Li+ pin?