well, I'm using a car batter to power up a monitor (230V) and a BBB at the same time.
BBB is powered through a LM2596 switch mode regulator. (12V -> 5V)
Monitor through a 100W inverter. (12V -> 230V)
It seems like BBB cannot generate a video output when both share the same battery.
Yes, the beagle is really boring in terms of external connections of anything.
I do not know LM2596 .. but I took a look at the datasheet.
I recommend you make an adjustable supply with lm317 +2 N3055. I made a recently, and is able to feed beagleBoneBlack cape + 4.3 ".
I hope this helps.;-)
Yes, you can do that too .. what is the input voltage to the regulator?
I think the problem with Beagle is caused by using the power supply used it to power other circuits. Are you doing it?