Why does your battery gauge go down when braking and car shuts off and blinker also makes a different faster noise?

Suspect low battery reserve (almost dead), alternator may not be recharging battery either due to low battery level insuffucient to energize alternator field windings or alternator/wire fault probable causing low battery in first place. Battery volt meter drops because alternator not recharging, Flasher speeds up when load drops through flasher, engine stalls because insufficent reserve on battery to run engine electronics. If battery ok to start motor: then suspect fault/connection in power wire to engine bay electronics or alternator. initial starting point from my diagnostic point of view