Feel free to ask all/any questions. That's the main purpose of these forums, as to share knowledge.
Many times, the alarm you are hearing, is the 12 volt low power alarm on your CO and/or propane leak detector.
When your battery gets low, these detectors will start alarming/beeping to let you know. The detectors (if not together in a combo unit) also have an end of life alarm sometimes, and you have to replace them if this is the case.
I have a feeling that when you are attempting to operate the slide, it tried to pull power from the battery (which is discharged and the reason the slide is not working) and may have briefly interrupted power to the alarming detector.
These detectors are also what we call phantom draws. When you are not connected to shore power, you battery supplies constant 12 volt DC power to these detectors. They will usually drain your battery also due to these phantom draws that many people do not realize. It'll pull my battery down in a week, if I don't disconnect the batteries negative cable or plug into shore power so my converter can charge the battery.
Here are some good articles I always suggest for those starting...and as stated, feel free to ask anything. Someone will always help.
This one touches on all the RV's electrical systems, including the battery.
Basic RV Electricity - RV Information (RV Maintenance)
and converter info
RV Converters and Amp Draw - RV Information (RV Maintenance)
I know in another thread, you discussed having a 2011 model RV you just recently purchased. You may want to check the battery out, as it may not be operating correct (or could be bad and not hold a proper charge)