Apple just seeded the second beta version of iOS 11.3 to developers, notably adding previously promised battery health monitoring features. Here’s how you can download it on your iDevice.

Note: This update is highly recommended as it improves the overall performance of the beta and squashes quite a bit of bugs. But if you are interested in jailbreaking, you are suggested to stay on iOS 11.2.2 firmware and below.

Please back up your iDevice as always before you restore to another iOS version. 

Step 1 Connect your iDevice to PC with USB cable and then launch 3uTools. 

Step 2 After 3uTools successfully connects your iDevice, navigate to "Flash & JB" -> "Easy Flash", there are compatible iOS versions options and please select iOS 11.3beta2 firmware. (Select the checkbox "Retain User's Data While Flashing" if you want to reserve data on your device.)

After you click "Flash", there will be a popup, read it deliberately and click "OK" to start flashing.

Step 3 Please do not disconnect your iDevice until the update has finished. It can take a few minutes. Your device will be updated to iOS 11.3 beta 2 and reboot once or twice during the process. 

After you upgrade, if you want to disable Apple's performance management features, please check here.