Hi I believe the V8 has up to 40 minutes runtime. The V8 has 2 power settings high power for day to day and general cleaning and boost mode for stubborn messages and stubborn spot cleaning. The boost mode uses the most battery power so the runtime is greatly reduced.  You’ll get the longest runtime in high power day to day cleaning and depending if your using a powered head or one of the non powered tools depends on the runtime too. 
It’s worth checking your V8 is not on boost mode as I believe they come boxed in that mode from new. This slider switch to change the modes is on the top on the main unit next to the post motor filter. This is probably why it’s needing frequent charging.

A great battery tip after using it before popping it back on charge let the machine battery cool for 5 minutes as they do warm up during use. This helps prolong battery life long term. 

Thank you,

I have had suction on max. I will try reducing it and see if that helps battery life. 

Your welcome.

That should definitely help with the battery life and runtime for general day to day cleaning.

There’s some handy tips on this post - How to: Maximise your cordless vacuum's battery life.