Processing Audit Part 1 (#22803)

Oh look at that, every modular computer in existence was always
processing at all times, regardless of if it was actually needed.
There's a couple more small examples I caught in my first pass, but all
of the rest are very low incidence. There are of course a very large
number of modular computers at any one point in time.

code/modules/power/cell.dm

@@ -21,14 +21,13 @@
 
 	charge = maxcharge
 
-	if(self_charge_percentage)
+	if(self_charge_percentage && charge < maxcharge)
 		START_PROCESSING(SSprocessing, src)
 
 	update_icon()
 
 /obj/item/cell/Destroy()
-	if(self_charge_percentage)
-		STOP_PROCESSING(SSprocessing, src)
+	STOP_PROCESSING(SSprocessing, src)
 	return ..()
 
 /obj/item/cell/process(seconds_per_tick)
@@ -41,6 +40,8 @@
 		var/recharge_for_this_process = round(recharge_amount_per_second * (seconds_per_tick / 10)) // divides seconds_per_tick by 10 to turn deciseconds into seconds
 		// finally, charge the cell
 		give(recharge_for_this_process)
+	if (charge >= maxcharge)
+		return PROCESS_KILL // No need to constantly process self-charging cells that are full.
 
 /obj/item/cell/Created()
 	//Newly built cells spawn with no charge to prevent power exploits
@@ -51,13 +52,12 @@
 	return src
 
 /obj/item/cell/drain_power(var/drain_check, var/surge, var/power = 0)
-
 	if(drain_check)
 		return 1
 
 	if(charge <= 0)
 		return 0
-
+	START_PROCESSING(SSprocessing, src) // Always attempt at least one process if the battery level is ever reduced.
 	var/cell_amt = power * CELLRATE
 
 	return use(cell_amt) / CELLRATE