Force "low power mode" on mac

When there is less than 5% battery left on a mac, the battery indicator goes red and system performance significantly drops - presumably in an attempt to make that remaining 5% last a little longer.

Is there a way to manually trigger this, so that the system performance is low (and battery life longer), even when there is plentiful battery?

This would theoretically be a way of extending the number of hours on a battery beyond the rated amount.

I'm using underclocking app volta, seems to be working so far.

Energy Saver preferences

The easiest way to manage your power consumption on a MacBook model is to use the Energy Saver preference Pane.

1. Go to Apple > System Preferences
2. Select the Energy Saver preference pane
3. You'll now have access to a range of settings.
4. Since you're interested in reducing power usage while on battery power, select the Battery tab.

NOTE: The options you'll have here will depend on your Mac model and version of macOS. For example, models with both built-in and dedicated graphics cards will provide a graphics switching checkbox that configures your Mac to automatically switch between graphics modes to improve battery life.

Display brightness

The most obvious other factor that can reduce battery consumption is reducing the brightness level of your built-in display. You can access this from Apple > System Preferences > Displays.

Further reading

You may find the following resources useful:

• Use the Energy Saver settings on your Mac
• About Energy Saver sleep and idle modes in Mac OS X

Just adding to Monomeeth's answer:

• Quitting all applications not currently needed or in active use
• disabling Bluetooth and WiFi, if possible
• disabling as much options, services, background processes etc. as possible (anything related to syncing, overcrowded Notification Center…)

Lowering the Processor Speed:

• and closest to what you directly asked: disable at least TurboBoost on the main processor with e.g. Turbo Boost Switcher. That will keep your CPU cooler, less Watt-hungry and, if you have fans, keeps your fans down.

Note: This expands on the previous answers by LаngLаngС, Monomeeth, and diegoalberto.

My understanding of the Low Power Mode feature on iOS is that it affects three main areas:

1. Display: reduces the brightness of the display, and limits how long it stays on while inactive (30 seconds)
2. Performance: reduces the performance of active foreground tasks, and significantly reduces the performance and frequency of background tasks
3. Network activity: stops nearly all background network updates (e.g., it stops fetching email automatically, or pre-loading the latest posts in your Facebook news feed)

So, here’s what you can do on the Mac to manually replicate this functionality:

1. Display:
   • turn down the screen brightness
   • use the Energy Saver panel in System Preferences to adjust how quickly the screen turns off when you’re not actively using your computer
2. Performance:
   • disable the Turbo Boost CPU over-clocking feature (see What is the new turbo boost in the MacBook line?), using an app like Turbo Boost Switcher (free and paid versions available), or Volta (paid, with a 7-day trial)
   • limit how much physical electrical energy (watts) the CPU is actually allowed to draw, using the Volta app mentioned above
   • if you have a MacBook Pro, force your computer to use only the slower, “integrated” GPU for graphics—instead of the faster, dedicated (“discrete”) GPU—with an app like gfxCardStatus (free) [note: there are some limitations for when this is allowed—the discrete GPU is still required by some apps, and for using external displays)
     • on Macs with this dedicated, discrete GPU, the Energy Saver panel of System Preferences does have an option for automatic graphics switching that is on by default
3. Network activity:
   • besides just turning off WiFi and Bluetooth, you can also limit which apps are allowed to use your network connection, with an app like Trip Mode (paid, or as part of the Setapp subscription bundle)

Example: In 2018, Marco Arment wrote a great little piece explaining how useful it would be to have a “Low Power Mode” feature on the Mac. By experimenting with the Volta app to disable the Turbo Boost feature, and limit the amount of energy (watts) the CPU was allowed to use, he was able to get up to 50-100% extra battery life, depending on the setting he used.

Other common tips:

• Software:
  • keep your apps and operating system as up-to-date as possible, especially when major new versions are released
  • use the built-in Activity Monitor app to monitor which apps are using a lot of resources (especially the Energy tab, with the list sorted by Energy Impact)
• Hardware: (not applicable to all Macs, especially newer ones that can’t be upgraded after purchase)
  • if you are using an older, mechanical (spinning) hard drive, replace it with an SSD (solid-state drive), which will not only be much faster, but require less power
  • if you use a lot of apps at once, or apps that process a lot of data, or use a lot of browser tabs, upgrade the system memory (RAM)—when it gets full, the system has to save temporary data to the hard drive instead, which requires extra processing (you can always monitor memory usage in the same built-in Activity Monitor app)