How can I disable the low battery alarm?

If you have already disabled the setting in BIOS and the deactivation of the modules does not help, as described below, then you probably have a bug in the BIOS.

Disable the internal speaker:

sudo modprobe -r pcspkr snd_pcsp

For a permanent solution, edit /etc/modprobe.d/blacklist.conf

sudo nano /etc/modprobe.d/blacklist.conf

and add/change

# low-quality, just noise when being used for sound playback, causes
# hangs at desktop session start (Ubuntu: #246969)
blacklist snd_pcsp

# ugly and loud noise, getting on everyone's nerves; this should be done by a
# nice pulseaudio bing (Ubuntu: #77010)
blacklist pcspkr