Thats why im saying, just having the tip covered in new metal should not make the drill store more energy, the recipe should include more components "Electric" wise to allow to do that. But let me clear my head a little and later today i will give you a more proper response/idea/suggestion for it.
Oh to clarify, my drills aren't just tipped, these you build entirely. 5 metal bar + circuit + battery. Similar to the base mining drill.
Although I may allow the players to diamond tip each one to increase their speed though.