I have a 720A Dittle radio
Power requirements;
Receive .1 - .4 amps
Transmit (tone) 1.4 amps (.8 amps unmodulated)
The 11.8 volts I was referring to is before transmit.
If I remember correctly when the battery is fully charged
and I hit the transmit button the voltage drops from 12.7 to 12.2.
Udo

With the battery run down to 11.8 volts, measure the voltage right at
the radio connector while keying the transmitter for 5-10 seconds. If it
drops more than it does when the battery is fully (or nearly so)
charged, the problem might be the battery.

However....
I found a German manual for the ATR720A (and ATR70C in English) on the
Filser site (I think they took over the radios from Avionic Dittel).
The specifications don't make any mention of what voltage range the
radio will function over, so I suspect 12 volt battery operation wasn't
on their minds when it was designed. This appears to be an older design
radio, and likely is one that would benefit from 14 volt operation.

So, if it's not the battery, your choices seem to be a modern radio
(like the Walter Dittel FSG 2T I mentioned) or going to a 14 volt
battery pack. Or waiting till you get closer to the airfield to make
your call :^)

Eric Greenwell

I have this Radio now for many years.
Based on what you and Tim are saying, I concluded that
this radio does not perform very well at lower voltage.
Only in the past couple of years while flying a glider with restrictive
space for a batteries (the standard 12v 7amp) have I noticed any
deficiency at low voltage even with fresh sets of batteries.
also this radio seem to eat more on stand by.
Prior to this I had no restriction in capacity and the problem never
came up. Other then that the radio works fine and has good range
when the voltage is up.
Thanks
Udo