How much battery life does google maps use on my iPhone 4S?

I have a long journey to make and my Sat Nav won't work in my car as I can't power it up at the moment, so I can use Google maps on my iPhone but need to be sure the battery will last the whole journey!

The phone is a year old so it's not a brand new battery when they actually last a while!

I know I can close all the apps I have open by double clicking the home button but still wondering if it'll last!

Maps require locations services that use a lot of battery see here:
http://appletoolbox.com/2013/01/google-map-apps-causing-your-iphone-battery-drain-to-fast/

Most cars have an accessory socket which you can plug into and then your phone will have all the power it needs
I do this with my phone when using maps etc and I'm in the truck all day