I have not installed any other app on my Samsung Note 3 (SM N9005 Android v5.0) for a long time so I am familiar with how quickly the battery runs down.
After installing Zoiper (1.30) and registering with my provider I noticed immediately that the battery was running down a lot faster. Then I set Zoiper as inactive so that I could register my computer to receive and make calls instead. The battery continued to be consumed seemingly as before.
So I did a 'force stop' which has put matters back to how they were before installing Zoiper.