Borescope battery hack that saved my Tuesday inspection

I run a small one-man shop out of hangar 4 at KPDX and my old borescope kept dying mid-inspection on a Cessna 172 cylinder. The company wanted $180 for their replacement battery pack so I grabbed a generic 12V drill battery off my truck, wired up a pigtail to the scope's DC input, and taped it to the handle. Worked for the full 45 minute check and I've done it three more times since. The image quality stayed clean, no flicker, no heat issues. I was skeptical because the manual says use only their adapter but this has been rock solid for 6 weeks now. Anyone else running off-brand power on their test gear or am I the only cheap one here?