Turn screen brightness down, put screen time out on lowest setting, use default theme, turn off vibration and close apps not in use. That's just a start. I get approx a day and a half now because I use my PlayBook for just about everything except for phone calls and text......I have a boring life
Make sure apps are closed.
Turn GPS on e911.
Hit the standby button at the top when you set your phone down.
Set social networking apps to only fresh upon opening app.
I'm with spencerdl; since I got my PlayBook I do all my browsing, media etc on the PlayBook. I use the BlackBerry handheld for calls, messaging, Music and GPS when driving.