The electricity our brain makes barely makes a light bulb work...
considering they had a few billion, your argument is somewhat invalid.
that and remember they're in a computer simulation, it might have hightened mental use, which would increase the electricity produced.
Which makes me think: If we could actually harvest the electricity produced by the brains of half the human population... we could make a lightning bolt with our heads. Maybe.
On the topic of charging devices with out heart, I guess we could do it by implanting some valves or something in the middle of the main arteries and veins right next to our hearts, and have the blood go through them before leaving/entering the heart. And then have some really high tech stuff connected to these valves/pipes/whatever which harvests energy obtained from the blood moving through the valve, and converts it to electricity.
Or, make the electronic stuff out of human cells, and pump blood through it. Making something a cyborg, but not from human to robot, from robot to human