Using lithium-ion battery as power supply

Hello, i have 2 of these batteries.

and i got an universal charger for the battery. the universal charger have usb output too.

I was thinking if i could use this somehow as an power supply to my arduino Uno?
if yes, how?

What's its output voltage level?
Can you add a connector to it easily?

oh throught that sony had written it themself.

battery info:
3.7VDC
1900mAH
Lithium-ion battery
Model: BA800

Charger info:
Input: AC100-240V 50/60Hz 150mA
Output: DC 4.2V 350(+-)50mA
Output(usb): DC5.2V 800mA

i can take pics of the items too if needed.