Here is a board with answers to commonly asked questions about the RP2.
OTA Upgrades 
Q: Can I not upgrade OTA? The current version addresses my current needs.
It is recommended to upgrade. RP2 will be continuously optimized according to customer needs, and the optimized content will be updated via an OTA.
Q: How do I upgrade via OTA?
Open it up. Here's a detailed tutorial. https://drive.google.com/file/d/1qz3H2imk2peb4tHcqSLIGf7OdcVpHAdl/view?usp=sharing
Q: Can I uninstall Upgrade Repair APK?
Of course, Upgrade Repair APK will no longer be required when your system has the Upgrade APK.
Q: Can I use the original SD Card to install this file and switch to the 128 GB Internal Storage Card?
Yes, OTA download is stored on The SD Card, so you have to insert the SD Card, after the update, you can switch to your internal SD Card.
Q: When I select "Check Update", why does the signature verification fail?
Please contact your seller to confirm that your signature is activated.
Q: Why was my Android system emptied after I upgraded to 8.1/Lineage OS?
Before you upgrade, it's version 6.0, and the apps and data aren't compatible with Android 8.1/Lineage OS, so it will be cleared.
Common SD Card Problems 
Q: How do I add games?
Retroid OS: Place your games in the SD:\Games\ directory. If you don't see your games after adding them, press the home button to enter the Settings, enter the Game Settings, select 'External Game Management', select your ROM type/file and press A to add it. Android OS: Place them into your file directory like this: SD:\ROMs\corresponding game type.
Q: Why does my SD card still have storage space, but it will prompt that I have insufficient memory and fail to transfer files?
Because we downloaded files onto it first and installed them; it took twice as much space to complete, and we left some free space to keep it running properly.
Q: Why can't I see my SD Card when my RP2 is plugged into my computer?
To view the contents of the SD card, you need to remove the SD card and plug in an SD Card Reader to connect to your computer.
Q: I accidentally deleted my SD Card's files/formatted my SD Card; what do I do?
Copy this to your SD Card: https://drive.google.com/file/d/1Li1LR9Lc9-cMIFtM7UXWPB8oDDTPqtAi/view?usp=sharing
Q: Can I exchange the provided 32 GB SD Card for a larger one?
Of course, but please note that the largest card in our official testing is 128 GB. If you use a larger card, there may be some minor issues.
Common Battery Problems 
Q: How long does it take for the battery to be fully charged?
It takes 2.5 to 3 hours to fully charge.
Q: I still can't turn on my handheld after charging it.
After entering battery protection, the RP2 needs to be charged for 6-12 hours before being booted. Usually, the battery protection is caused by excessive battery exhaustion, but other external factors can cause it to enter this state.
Q: I just got my handheld, but the battery drains pretty fast.
Don't worry, the battery just isn’t calibrated yet. Just charge it completely and drain it a few times naturally.
Q: How long will my battery last when fully charged?
Retroid OS: About five hours. Android OS: About three hours.
Q: Can I play my Retroid OS library on Android?
Retroid OS and Android are separate operating systems, so no.
Q: Can Retroid OS can be updated separately?
No! Android can't be updated separately either!
Q: Why can't I save my game(s)?
Not all games can be archived; if the archiving feature fails, it is most likely be related to that specific game.
Q: I suddenly can't get into the game market.
Check whether your SD Card is inserted correctly, whether your network is smooth, and restart the RP2. If you still can't solve your problem, please contact Retroid customer support.
Q: I didn't plug in my headphones; why is my device saying they're connected?
This is a small internal bug, but it will not affect normal use.
Q: How does the search function work? Why can't I find a certain game?
Certain games are searched by pinyin (Chinese) initials, while others are searched by keywords.
Q: I want to delete all of my games. What's the password to do so?
Q: Will Android be upgraded to Android 9 or Android 10?
There will be no major operating system updates after 8.1., but 8.1 will continue to be optimized by the community/developers through official OTAs and CFW.
Q: Why do I have delay and lag?
Too many programs running in the background can cause lag, so close unnecessary apps in the app switcher.
Q: I didn't plug my headphones; why does my device say they're connected?
This is a small internal action, but will not affect normal use.
Q: Why do my emulators run so slowly? The Task Manager shows 50% CPU usage even when idle.
The process "android.process.media" might be indexing thumbnails and boxarts on the SD Card. You can prevent the indexing by adding an empty ".nomedia" file to the SD card.