9v USB LED light

I had a cheap heavy duty battery in my fluke meter that I put in it because I was out of alkaline batteries and it finally showed up BATT in the display so I took it out and checked it on my battery tester and it was between 5 and 6 volts. I had a cheap dollar store LED light but it was flakey and suddenly I thought I have these cheap USB LED modules with 3 SMD LEDs in them so I took a pair of alligator clips and connected it up to the depleted 9v battery and it puts out plenty of light. I assume it will run for weeks like this so I've considered making a USB 9v battery setup. It is a lot cheaper than buying one of those 9v clip on LED light heads as I paid about 50 cents for the USB LED module you can get some cheaper if you order 5 at a time from some dealers on ebay. I've found some of them full power on a power bank only draw about 30ma I figure that as the battery depletes the current will drop to sub ma levels and run for another week. I wouldn't recommend trying this with a less than depleted battery however as the voltage may not drop to safe levels for the USB LED module.