I've only ever used non rechargeable cells in the pack.
I have it sitting in flight bag ready for use, with the headset adapter cable tied to the unit.
I've used it at our fly in for A/G comms when not on the main radio, it worked on the cells for a good length of time with no need to replace.
I've replaced the batteries twice in the couple of years I've had it.... There is a battery indicator on the screen that shows when the batteries might need replacing as the level drops down on transmit under load when they do.
The voltage on the batteries when on load is difficult to measure due RF but with the unit still working but showing near empty on TX I estimate about 1.28v on load and off load (recieve) the batteries were showing 1.35v.
New batteries measured 1.61v off load (Duracell Ultra Power).
If your really worried about cells going flat, you could pack some spares in your bag or even buy a spare bat pack ready to clip in.
Did I mention our Breakfast Fly In
is on the 5th August?
The views I express here are entirely my own and are not intended to represent my employer.