Started experiencing this problem recently when driving. The car will just die, engine, electrical, everything. Did some checking and something was draining the battery when the car was not running, so I tested multiple things. Alternator is fine. The DCC fuse appeared to be drawing a lot of current so I removed it and the car would hold a charge and start. Appeared to be OK for short test drives but then it happended again. Car will run fine when left idle, radio, a/c, lights all on and functioning. What I've noticed is, when the car is running idle, and I press the brakes, it appears to draw a lot power, lights dim, a/c power decreases. If I keep the brake pedal depressed, power continues to decrease and the ABS light will come on and the batter light will come on. The car doesn't die when idle, but does when I drive it.

 

Look around for an ABS fuse. Pull the fuse and determine if the power still drains when pressing on the brake.

Obtain a low cost voltmeter that has an amp indication function. Check for amps between the battery and battery cable when the engine and all acc are off. If higher then 200-300ma.

DCC may power the Dome, ECU-B and Radio No 1 circuit fuses (if the car has these). If you have these fuse pull then one at a time to determine if the power drain when engine decreases.