recording with audacity using battery

I have been doing some recording with audacity using laptop on a battery. This will give me about 3 hours of recording if i turn off the display. Since this laptop can idle over 6 hours, i have been wondering if there is any way to extend the time it can record on battery with some settings. I already undervolted my cpu but that didnt give me any improvement since while recording cpu is basicly idling anyway. I turned off wifi and bluetooth, so basicly my question is, what can i do inside audacity (changing settings) that will net me more recording time using laptops battery ?

I doubt that any settings in Audacity will have a significant effect on the available recording time.

Use an external battery?

Some laptops can run on 12V. If not, use a 12V + 6V lead/acid battery in series. That should be close enough for 19 V powered laptops.