Need help with camera

I have an old camcorder that I would like to use again but unsurprisingly the batteries are dead and don't get made anymore so I had the idea of attaching it to a USB powerbank. My current setup is probably a horrible approach but I'm using a cable that boosts the 5V to 9V and the I use 3 diodes in series to bring it back down to ~7V. This lets the camera turn on but it can't handle the power draw of the motors kicking into action. I'm assuming it's the boost cable that's probably limited to 1A. My new idea is to use a buck converter but I'm unsure how I attach one to a USB port.

Any advice on this would be appreciated.