ESTEBEVERDE
Veteran
The thing is if Evro observation is correct, just wiring another battery would not work; it looks like Panasonic designed in a voltage level interlock in addition to the communication one. Essentially, the AC Adapter puts out fixed voltage about 7.5V, if a 2 cell Li-Ion battery is connected, it's voltage is about 8.2V fully charged, causing the camera to shut off and display the message. Evro, did I interpret your test correctly? I do not have access to the 150, so can not verify this.
Actually if you read one of my much earlier post on using a 12volt for this system I specified step down to the requisite voltage.
I think he said the range is somewhere in the 7.1 - 7.9 volt spread.
It is absolutely doable.
But, each person has to evaluate their needs to see if it is worth the effort.