I have a rechargeable Icom that I keep in the charging cradle in the hangar between flights, and in the seat back during flights with a headset adapter, for radio emergencies.
Never had a radio emergency.
I've had a couple of NORDO incidents though I'd not characterize them as emergencies. In all cases it wasn't the radios themselves that went out but the electrical system driving them.
In one case I got a green light from the tower. In most of the others, I just went into an uncontrolled field.
In one case, I was in the backseat and after the student in the left seat bungled the call to IAD approach about the loss of electrics, the instructor told him to give me the radio. Alas, the King KX99 had a nearly dead NiCad pack which wouldn't allow me to transmit (at least not that was heard by anybody). Fortunately, the controller heard enough of the first call to understand. First, he tried to relay to me off incoming airliners (no joy). Then I get:
IAD: 4SP, we have a primary only target 20 miles NE of the field. If you believe that is you, turn to heading 270.
(I beat on the instructor's (he's the one flying at this point) back and shout, turn to 270 and he does).
IAD: Very good, 4SP if you'd like to come to Dulles, turn to heading 210
(I yell 210 at the instructor. This puts us on a direct heading toward the runway).
IAD: 4SP you're cleared to land, any runway. If we don't hear from you, we'll roll the equipment.
ME: We don't need the equipment, 4SP.
IAD: Very good. (yea! they heard that).
I wasn't able to reach them once we landed. The radio was now completely dead. We taxied in. The instructor set to debrief the student while I called the tower to thank them for their assistance.