Viber in background and Viber

[Sone3D]

* DON’T KILL YOUR VIBER: To make sure you always get incoming calls/messages notifications, we strongly recommend you to keep Viber running in the background. This does not drain your battery or use up memory and improves your Viber experience.

What about battery drain with this?

 

[Pooshka]

What about battery drain with this?

Did you read your own quoted text? It answers your question right there.

Now if you wanna know how or why it does not drain battery, that's another question.