The amount of time needed to grind 5 charges is in no way comparable to the trash you get from a Tier 3 engram. I've focused two now and both drops were garbage, and in no way worth the grind. It should have been 1 charge per tier (e.g. 1 for Tier 1, 2 for Tier 2, and 3 for Tier 3). Battlegrounds is fun, but it's probably the grindiest seasonal activity Destiny has ever had. If there are any more challenges that require Tier 3 engrams, I will be skipping them.