Stop MacBook Air sleeping when lid closed and on battery

Hi

I have a 2016 13" MacBook Air and El Capitan v10.11.6 which I use for work. I need to close the lid to move from meeting to meeting but I need to keep network connections open and therefore need to stop the machine from sleeping.

In System Preferences, Energy Saver I see there is an option for 'Prevent computer from sleeping automatically when the display is off' but this is only available on the 'Power Adapter' section and is not available in the 'Battery' section. I need to stop it happening while on battery too.

How can I keep the system active when I close the lid on battery please?

Thanks.