LaughingD has a good idea on it, but I think you could do better. I''m sure you need a seperate function for it, but the 100% thing only works if you take it to 0% once fired. The game would have to update this versus a timer for sure, but the problem is that you tend to lose out somewhere depending on design. If you check once per second of time passed, then you lose or gain some ability to use the weapon simply cause the player could fire it at a half-second interval. Without a timer for the gun, you run into a problem of either incrimenting it this next time around (since it was made to less than 100%, it would show up as needing upped if you follow LaughingD''s method), or you don''t and incriment it next time, since it was fired this round. Either way, the player loses or gains a half-second. If you could feasibly fire at 9/10 of a second, and it upped at every second.. you''d actually find yourself able to fire faster than the game is supposed to let you You''d be gaining that 9/10 back instantaneously.
What you should do is have a timer for each, but in a different way. If you keep a "last fired" time then you should have no problems incrimenting it. If each weapon were to be loaded into memory and constantly active, this would be the perfect solution. This would mean that the weapons are able to call upon the timer and compare it to their last fired times, as long as readiness is below 100%. You could make it incriment readiness at any interval you wanted, and it would ensure that they all incrimented as they should.
A combination of both is possible.. in that you have a timer on them all which every second, checks the ammount of time lapsed, and incriments as nessicary. When they''re at a place where they need less than a full second to increase, have it reupdate at the time needed.. that way it goes to full at the correct time without losing time, even if that time is a fraction of a second. Those franctions can add up.. either for or against the player depending on how you work it.
It takes a lot of math to do this, and some pretty hearty functions basically, you''ll have to figure out how long you want each weapon to recharge, if it''s 3 seconds.. each second adds 1/3 to the ammount of readiness of the weapon. In this way, if you had fired at a half-second, then at the next update second.. you would gain 1/6 back, and then the next second you''d get 1/3, and then another 1/3. This leaves you with 5/6. Now, knowing you gain 1/3 per second, you have to figure out how much time you need now. Now, 1/3 per second means (1/3)/1 if you set (1/3)/x = 1/6 then you can work out that x is 1/2. And then the computer can update in a half second to get the gun to full readiness as expected.
I admit.. this is a lot of work for something most people won''t appreciate.. but it all depends on how picky you are It could be possible that the program takes longer to find the answer to X and thus it doesn''t really matter either way. lol
The individual functions for weapons are really nice, as they allow the weapons to be loaded modularly into memory. If you coded it well, everyone with the same type of weapon could refernce one memory point to find the guns stats. They would jump off a pointer to their individual gun stats, such as last time fired, readiness level, etc. This is optimal! By having all units referencing a single point in memory for gun power, range, etc.. you keep the footprint of the game to a minimum, so the game can have time for all the graphics you want
if you notice, mech games don''t show a status bar for readiness, the weapon is merely dimmed out or green to represent it can fire. I would suspect most major companies use something that just checks each second or half second.
This is prolly the easiest way.. but i provided alternatives which would be useful to people who try to push the limit of the game like me!

J