>>325663680
>do rechargables have slightly lower voltage sometimes?
Yes. Not only do they come in a range of voltages but the battery market is rife with misleading advertising. Cheap or improperly charged ones can be inconsistent with voltage and if charged ones sit on a shelf for years they can lose a lot of their capacity. Oculus recommend 1.5v which is common but most budget 'long life' ones will be below that at either 1.3v or 1.2v. 
I have a 1.2v pair that seem to work fine in my Rift S controllers but there are many examples of people on Quest1/2 who had tracking issues until they switched to better batteries.