Trying to battery operate Icom IC735 I notice that if the voltage drops below 11V it has modulation problem. Searching the circuit diagram I notice that a 78M08 exists that requires exactly 11V to operate without loosing regulation. I found the low dropout 78R08 that requires only 0.5 to regulate. The 78M08 exists at the MAIN pcb. After removing all cables and 78M08 it needed to grow the hole with 1mm drill near the 13.8 input of the regulator in order to fit the 78R08 properly on the existing hole. It is needed also to cut the PCB of the other two contacts near the hole (see the red circles) in order to avoid short circuit. Before placing the 78R08 the 4th pin must be bended and soldered to the 1st pin. Then silicone grease for cooling is added and placed at the hole, fixing the screw. The 1st pin is bended carefully and soldered to the 13.8 pad. Then you bend very carefully the 3rd pin to the ground. If this pin is cut for any reason 13.8V will pass to the 8V !!! Then solder the 2nd pin. Then the flux must be cleared.
Testing with a lab power supply it was noticed that can operate now with 10V. Below this voltage it may stop working the unit and it must switched off and on to operate again. It was operated USB with full power instantly with a new 7Ah Lead Acid without problem !!! Depending of the internal resistance of the battery it can be operated without problems if the negative edge is over 10V witch is a safe margin for a Lead Acid battery.