Whatever you are doing in windows, if it's processor intensive it will drain the battery. Just having the VM run and do nothing really doesn't drain battery. I recommend use the 'longer battery life' setting in virtual machine settings (Configurare the virtual machine, under options, there is an option on the left pane called Optimization). Parallels Inc., a global leader in cross-platform solutions, makes it simple for customers to use and access the applications and files they need on any device or operating system. We help businesses and individuals securely and productively use their favorite devices and preferred technology, whether it’s Windows®, Mac®, iOS, AndroidTM, Chromebook, Linux, Raspberry Pi. Parallels Remote Application Server; Parallels Desktop for Mac Business Edition; Parallels Desktop for Mac Pro Edition; Parallels Desktop for Chromebook Enterprise; Parallels Mac Management for SCCM; Parallels Desktop for Mac; Parallels Toolbox for Mac & Windows; Parallels Access.

Why MacBooks loose charge in sleep mode? The answer is because MacBook is not entirely asleep, it’s doing something. Whenever the MacBook performs some tasks, it’s losing charge because it needs the energy to perform those tasks.

If MacBook’s battery is draining while it is sleeping, it happens for two reasons: the Mac gets awakened periodically by an external event (network, Bluetooth signal, or peripheral hardware), or there is an application that runs on the background that does not let MacBook go to sleep.

To fix the problem you need to find the app or process that keeps the Mac awake even when you close the lid.

However, every Mac environment is unique. You and I have different apps installed, so it is hard for me to tell which applications are causing battery drainage. In this post, I will provide tools to explore and find rogue apps or processes running on your Mac.

We will try to fix the battery issues in 4 days or less. Each day we will try progressively more advanced techniques. While I hope we wouldn’t need to resort to the most radical remedies, at some point, you may need to try something out of your comfort zone.

But before we start, let’s understand that you may always have some little battery discharge. What I want to say, if after Day 1 the battery loss changes from 30% to 5%, it may be not worth to keep pushing and implement Day 2 techniques. You need to know when to stop.

Day 1

On day 1, you will try everything that does not require special skills. Since we are going to change many things at once, if even one change works, we wouldn’t know what exactly which change fixed the issue.

If you like to make minimal changes to the MacBook Pro or MacBook Air, implement only one change every day and verify next morning if the fix was efficient or not. If the change did not help, you could revert it.

But, if you want to get it done as soon as possible, then it makes sense to apply all fixes in one day. And it’s exactly what we are going to do. We will cram all possible changes on the first day and measure it the next day.

Scan for viruses

What? Didn’t you know that Mac can get a virus? Unfortunately, this happens. If you want to find out more about Mac virus and ways to protect your laptop from them, check my article:

Today, I want you to install either Norton 360 for Mac or Mac Internet Security from Intego and run the scan.

Why these two? I tested 117 malware samples on my MacBook and only these two programs were able to detect and remove all viruses.

Why does this work?

The goals of any malware are:

Do damage to your computer.
Hide, so you can’t find and delete it.

When malware is running, you may not see anything on the screen. Even when you think you closed all apps, the virus may still be running in the background and draining the battery.

On the other hand, if you already have an active anti-malware protection, there is a possibility that the antivirus is using energy. We will see how to find out this in later sections.

Check battery state

If the MacBook is several years old, it is possible that the battery does not hold a charge as effectively as before.

The easiest way to check the battery state is by holding Option (Alt) key and clicking on the battery icon in the top right corner of the screen.

Obviously, for this method to work, you must have a battery icon configured to appear on the screen.

Below is the screenshot from my MacBook Pro.

As you can see, the state is Normal. This is what you want to see on your MacBook. There are other states besides Normal:

Replace Soon
Replace Now
Service Battery

To find what each state means and other battery-related things (battery life cycles, battery capacity and ways to preserve MacBook Pro battery lifespan) check my post:
Should I Drain my MacBook Battery Before Recharging

Why does this work?

If the battery is in any state other than Normal, it’s time to replace it. There is no point to continue with changing the system if the hardware is failing.

According to Mac Service and Repairbatter replacement will cost you between $129 and $199 in the US.

Run OS updates

Open System Preferences app.
Click on Software Update pane.
Wait for Mac to check if there any updates available
If there any updates, then open the App Store and click on Updates.

Why does this work?

macOS updates sometimes have fixes for battery usage. If there was a problem with the OS, you want that fix installed.

Start in Safe mode

What is Safe mode?

When MacBook starts in a safe mode (also called safe boot), it does not load many things that generally run on start. For instance, if you have the DropBox running on startup, it will not load automatically. Also, most external devices will not be available; graphics may be slower, wifi limited, etc.

Why does this work?

By itself, safe mode is not very useful. After all, why would you run your MacBook in a reduced fashion? However, the booting in the Safe mode triggers some internal checks, which may cause some issues with the MacBook performance. All you need is it to boot in Safe mode and then restart in a regular way.

How to boot in Safe mode?

Reboot MacBook.
Before MacBook starts, press and hold the Shift key.
When the Apple logo appears, you can release the Shift key.
Log in.
Reboot again (without holding Shift key).

Exceptions:

If you have FileVault enabled, then you need to enter the password twice.
If you have firmware password enabled, then first disable the firmware password, reboot in safe mode, and turn the password back on.

Reset PRAM/NVRAM and SMC

All MacBooks have some vital settings saved in PRAM (Parameter RAM) and NVRAM (non-volatile RAM). Sometimes the data in those memory pockets gets corrupted, and the MacBook Pro (or Air) starts misbehaving. Apple recommends resetting those settings when you think there is an issue sound, display, disk, etc.

Similarly, Apple recommends resetting SMC (System Management Controller), which is responsible for many things and among them Battery Management and Thermal management. The most important for us they suggest resetting SMC if:

Your computer’s fans run at high speed, even though it isn’t under heavy usage and is properly ventilated.
Your Mac notebook doesn’t respond properly when you close or open the lid.
The battery doesn’t charge properly.

There are detailed instructions on resetting PRAM/NVRAM and SMC from Apple, so I am not going to repeat them here:

How to reset the System Management Controller (SMC) on your Mac. Note that there are different instructions for MacBooks with removable and non-removable batteries. Also, MacBooks with T2 chips (2018 and later) must be handled differently than older Macs.

There are two things I want to add to those instructions:

Similar to Safe Mode resetting PRAM does not work when a firmware password is enabled. So, first, disable the firmware password, reset PRAM and SMC, and turn the password back on.

Many people report that they had to reset settings multiple times, sometimes up to 6. Since, you don’t have a visible problem such as a black screen or lack of sound, to verify that resetting worked, I suggest to repeat the procedures several times just in case. In other words, reset PRAM two times and then reset SMC at least two times.

Disable Power Nap while on battery power

Power Nap is a great way to have your MacBook do some useful work while it is not in use. When MacBook is in Power Nap state,

Parallels For Mac Drains Battery