both the charger and the batteries should work.
a 7 cell will need 10.5v to 11v at top of charge to get full.let it charge overnight and measure while still charging.
Thanks, I thought it would be simple, but it often is not as simple as at first glance. But there a couple of 9 V NIMH on the way, and if they are charged I will see what it will do. The stun gun is over 20 years old and I never needed it so won’t go to much more trouble, except to learn something.
Jerry
if you learn something its all good.and you now have 2 9v for the meter that gets left on.
that is after you tire of playing with the noisy ozone producing toy.
The school of hard knocks. 
But it could be worse.
Jerry
the ebl 9v li i had may have been a counterfeit.
it did not have any board in it.
and it was turning itself from a rectangle to a cylinder.
it was in of all odd things a vintage pocket radio.
the 2 cells were ballooning badly.
i should have taken pics.
i left the phone to charge in the truck and the cells were leaking so i was more interested in getting rid of it.
as far as ebl my limited experience lately has been good.
20650 and 26650 are good.