Place it at the exact cut where a character notices the power dropping, before any reaction line. Follow it with a classic error sound if the device then fails, or keep it solo before a cut to black for a cleaner end.
About this sound
This is a short low battery alert from a Wiko phone running Android 5.1, lasting just over a second and playing an error-style tone twice. It feels urgent and nagging, like a final warning before the screen goes dark. It comes from that Wiko handset's system sounds for low power.