Gotcha: That's not how it works in this game, unfortunately.
Every item has a 'quality' number. For wands and staves this quality number indicates how many times you can use it.
These quality numbers were manually given to these items by developers when they were making the game, and they are different for each wand/staff.
One wand could fire 10 times and run out, another wand could fire a hundred times. They all have different values.
The only way to check how many charges a wand/staff has left is by using Exult Studio and checking every item manually.
I wouldn't worry about it though. Firedoom staves generally suck. Their bolts move slowly and they cause more damage to your own party members than enemies.
