Everyone needs a bootable USB plug with DOS.
It boots in 10seconds, then doesn't do anything.
But, if your charging circuits are working properly, it will goose-start the old Li-on batteries.
I found that a dead battery (0 volts) will charge up to something (+volts) in seconds.
However, it will not retain that voltage very long. The older it is, the shorter the time.
That explains why it may light your flashlight, but almost immediately go dim.
Most charging-circuits are the goose-start type where they give the battery a jolt, then measure, then another jolt, then measure. The higher the measure, the less the jolt. Until a smooth voltage is attained.
Some laptops will actually show the charging light 'jolting' the battery.
Now that I told this story, ignore it.
Li-on batteries burn so hot, and explode so violently,,, you have no idea.
Replace the old battery with a know good battery. ( That excludes a 'new' battery.)
This will show if the charging circuits are working properly.
Any reputable repair shop can easily do this.