Q: my mighty mouse disconnects constantly after updating to el capitan version 10.11.2

Hello there, frankmeyers.

It seems you're having issues paining your Mighty Mouse on your MacBook Pro. The following Knowledge Base article offers up a few steps to consider for troubleshooting:

If your Apple wireless mouse, keyboard, or trackpad aren‘t working as expected

Your device isn't recognized by your Mac

Follow these steps if your mouse, keyboard, or trackpad isn't recognized by your Mac.

Make sure your wireless mouse, keyboard, or trackpad is turned on

The Magic Mouse and Magic Mouse 2 have a slide switch on the bottom of the device. Slide the switch to turn on the device. On the Magic Mouse, the green LED will briefly light up. On the Magic Mouse 2, green will be visible.

The Magic Keyboard and Magic Trackpad 2 have a slide switch on the back edge of the device. Slide the switch to turn on the device (you'll see green). Earlier Apple Wireless Keyboard models have a power button on the right side of the device. Pressing the button activates a green LED on the top of the device, near the button.

When you turn these devices on, they will appear as Connected in the Bluetooth section of System Preferences. If a device doesn't appear there, make sure it's charged or replace it batteries, and make sure it has been paired with your Mac.

Make sure your device has been set up to work with your Mac

Learn how to pair your Magic Mouse 2, Magic Keyboard, Magic Trackpad 2—and earlier models of Apple wireless devices—with your Mac.

Make sure Bluetooth is turned on

Choose Apple menu > System Preferences > Bluetooth and make sure that Bluetooth is turned on.

Refer to the table below for more information on determining the Bluetooth status. If the Bluetooth icon doesn't appear, or if the menu bar status continues to indicate that Bluetooth is off, restart your computer and then try to turn Bluetooth on again.

                                                                                                                                                                                        

Bluetooth menu icon	Bluetooth status
	Bluetooth turned on, but there are no devices connected to the Mac. See the Make sure the wireless mouse or keyboard is turned on section of this article.
	Bluetooth turned on and at least one wireless device is connected.
	When this icon flashes, at least one wireless device has a low battery. Click the Bluetooth icon to identify the affected device, then recharge the device or replace its batteries.
	Bluetooth is off. Click the Bluetooth icon using a USB mouse or built-in trackpad and select "Turn Bluetooth On"
	Bluetooth is offline or unavailable. Restart your Mac. If the Bluetooth status doesn’t change, disconnect all USB devices and restart your Mac again.

Make sure your devices are charged

Magic Mouse 2, Magic Keyboard, and Magic Trackpad 2 have built-in rechargeable batteries. You can charge these devices by connecting them to a Mac or a USB power adapter using a Lightning to USB Cable. For the fastest battery charging performance, be sure your device is switched on when connected to the Lightning to USB Cable.

To check the battery level of these devices, click the Bluetooth icon in your Mac's menu bar, then select your device by name. If the battery level of any device is low, recharge the device. If the device isn’t showing, make sure the device is turned using the steps outlined above.

Your mouse or keyboard intermittently stops responding

Follow these steps if your mouse or keyboard sometimes stops responding temporarily. 

Click or press a key

• Click the mouse or trackpad or press a key on the keyboard to reconnect the device to the computer. It may take a moment for the device to respond.

Check for signal interference

• Wireless networks that operate on 2.4GHz may cause interference. Move cordless phone base stations, microwave ovens, and other 2.4GHz electrical devices away from your Mac if you suspect interference.
• Keep wireless devices within 10 meters (approximately 30 feet) of your Mac.
• Avoid putting metal objects between your wireless device and your Mac.

Thanks for being a part of Apple Support Communities.

Kind Regards.

Hello again, frankmeyers.

Thanks for the clarification on what is occurring. Due to the nature of your question, it may be best if we get you in contact with someone who can look into this further. You may find more information by using another one of Apple's support resources - https://getsupport.apple.com

Cheers.