Yes, settings its charge to any number above 1 would fix it, but it would also deceive players. Now, it depends on what impression you want to give to them. Do you want to keep the 1 charge thing? If so, then use a trigger to detect when the healing wave item is used, and create a dummy, forcing it to cast the spell at the target unit. Otherwise, change the item classification to Miscellaneous, and set its charges to 0 - though it's going to be a permanent item.