Connecting Lego PF Motors to a Lego EV3
Connecting Lego PF Motors to a Lego EV3 is possible with a special adapter cable, the advantage of this is the ability to connect train motors and lights however, you do not get positional feedback on what angle the motor is at.
This uses an adapter cable that makes the EV3 think a large motor is connected.
The adapter cable can be bought on Bricklink (Bricklink x1676) or built from combining an EV3 wire and a Power Functions wire, with a few resistors.
In this configuration, the Power Functions motor is run from the EV3’s battery.
Power Functions Rechargeable Battery
This is a way of driving a Power Functions motor using the speed control on a rechargeable Power Functions battery pack.
It works by using an EV3 motor connected via an axle to a Power Functions rechargeable battery, then by rotating the EV3 motor to an angle, it selects a speed on the battery pack.
This has the advantage of separating the EV3 power battery from the Power Functions motor battery allowing for longer run times.
I use this technique on my GBC EV3 Truck.