Adds device powercells

Adds a type of smaller power cell for powering devices. Not used by much
at the moment, but it's one step closer to a more coherent picture of
power cells.

code/modules/mob/living/silicon/robot/robot.dm

@@ -594,6 +594,8 @@
 			user << "Close the panel first."
 		else if(cell)
 			user << "There is a power cell already installed."
+		else if(W.w_class != 3)
+			user << "\The [W] is too [W.w_class < 3? "small" : "large"] to fit here."
 		else
 			user.drop_item()
 			W.loc = src

code/modules/power/apc.dm

@@ -442,18 +442,21 @@
 		if(cell)
 			user << "There is a power cell already installed."
 			return
-		else
-			if (stat & MAINT)
-				user << "<span class='warning'>There is no connector for your power cell.</span>"
-				return
-			user.drop_item()
-			W.loc = src
-			cell = W
-			user.visible_message(\
-				"<span class='warning'>[user.name] has inserted the power cell to [src.name]!</span>",\
-				"<span class='notice'>You insert the power cell.</span>")
-			chargecount = 0
-			update_icon()
+		if (stat & MAINT)
+			user << "<span class='warning'>There is no connector for your power cell.</span>"
+			return
+		if(W.w_class != 3)
+			user << "\The [W] is too [W.w_class < 3? "small" : "large"] to fit here."
+			return
+		
+		user.drop_item()
+		W.loc = src
+		cell = W
+		user.visible_message(\
+			"<span class='warning'>[user.name] has inserted the power cell to [src.name]!</span>",\
+			"<span class='notice'>You insert the power cell.</span>")
+		chargecount = 0
+		update_icon()
 	else if	(istype(W, /obj/item/weapon/screwdriver))	// haxing
 		if(opened)
 			if (cell)

code/modules/projectiles/guns/energy.dm

@@ -14,7 +14,8 @@
 
 	var/obj/item/weapon/cell/power_supply //What type of power cell this uses
 	var/charge_cost = 100 //How much energy is needed to fire.
-	var/cell_type = /obj/item/weapon/cell
+	var/maxcharge = 1000 //the capacity of the weapon's power cell. Specifying a cell_type overrides this value.
+	var/cell_type = null
 	var/projectile_type = /obj/item/projectile/beam/practice
 	var/modifystate
 	var/charge_meter = 1	//if set, the icon state will be chosen based on the current charge
@@ -45,7 +46,8 @@
 	..()
 	if(cell_type)
 		power_supply = new cell_type(src)
-		power_supply.give(power_supply.maxcharge)
+	else
+		power_supply = new /obj/item/weapon/cell/device/variable(src, maxcharge)
 	if(self_recharge)
 		processing_objects.Add(src)
 	update_icon()