Have a tech look at the toner gauge nvm's. They were probably set to default when the battery died.
Did the tech fixing the non customer mode issue have any thoughts on the issue while he was there?
My 7525 type printers have had their toner dropping to 1% (always 1% and 268 pages remaining) very often, possibly every time though I can't confirm. The toner is clearly not empty, and usually will last for a while at 1%. This is the 006R01513 reorder number toner.
I'd assume this is either a software issue, or something to do with the black toner changing since it seemed to happen suddenly after a reorder a few months back.
Any idea how I can get my printers to stop giving the wrong readings?