Hello & Welcome to Just Answer,
Sorry I didn't see your question earlier and to hear of any issue you may be having with your system.
Without knowing the specific Make & Model of the system you have, it will be hard to give you specific information. But with that being said, almost ALL of the systems I have worked with have a "backup battery" attached somewhere close to the MAIN control box, and when the "lo bat" message appears and you hear the constant beeping, that tells us that the battery is "worn out" and needs to be replaced.
Again, not knowing the specific model, I can only tell you that the "typical backup battery" is a "gel cell" (or sealed lead acid), and can be mounted IN the MAIN control box (if large enough) OR mounted close to that box.
Let me give you a link to a video that does a very good job of explaining what you might expect to see, and how to select the correct battery for your application.
Click for Video --> https://www.youtube.com/watch?v=IOeQqXvwocE
Once you find the battery, you should be able to remove and replace it - without having to power down the system or doing any other reprogramming of the system.
I recommend trying to find a replacement battery LOCALLY - as they are usually HEAVY and shipping cost can be expensive.
Please let me know what you find or if you have any more questions.
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Thanks, ***** *****