Getting a battery meter to display properly is incredibly difficult. It's a hard task when you have a battery of known capacity, and known discharge rate and known charge rate."Dutch blog iCulture.nl, which spotted the battery icon's absence, speculates that Apple has removed it altogether because of persistent problems getting the indicator to display correctly."
The guess is because of Apple's technical incompetence.
It's even harder when you have a battery of unknown capacity, with an unknown discharge curve. The energizer battery from Lowes is going to have far different use characteristics than one from Dollar Tree. The one from Dollar Tree might even have a max voltage near or at the energizer minimum voltage.
I don't blame them for having trouble, but you'd think that they could sort of figure it out.