Other issue with rechargeables is that they have a flat voltage until they discharge. They sit at 1.2 (or so) volts over 80% of their capacity. Alkalines, however, reduce their voltage pretty constantly during discharge until they are dead.
What this means is that the device (such as a headset) has no way of knowing that the battery is soon to die when using rechargeables - so isn't going to warn you at the start of a trip.
Me - I use rechargables in everything except headsets!