I know my battery is good for 90 minutes, because I had it go black as I was leaving a property. If it is initially set for the screen to shut down after three minutes, to my logic that should extend the battery. Is that correct? If using the unit on audio only, is the record time extended? I purchased my unit in 2009.
I would assume that these should both extend battery life as it takes quite a bit of power to keep a screen lit up. However, I do not know for certain.
That said: I would find a 90 minute battery very difficult to use - I do quite a few back-to-back shops and periodically have video shops that run more than 90 minutes.... It might be worth your sanity to get a new battery: I have one that's good for six hours. I can use it all day, every day, if I am wise enough to plug it into my car charger when going from one place to another and recharge it fully overnight.
Hard work builds character and homework is good for your soul.
Thank you for your thought concerning the logic of both questions. As to an extended battery, I have only had back-to-back video assignments once and used my second battery. I do not accept any work that will require an overnight stay and my rates are such that only a company in need will consider me. Most of my work is local and self-developed.