Jimmy,
I just paralleled my house battery with another battery to boost my amp hour capacity. Both are new Interstate batteries. When I have my VHF, GPS, Fishfinder, and radar turned on and I try to run my washdown pump, the radar will shut off. Everything else stays on. I have the radar on standby not transmit. Shouldn't adding the additional battery prevent this? Could the high amp draw of the washdown pump cause a sudden drop in volts and that causes the radar to turn off? All my wiring and battery switches are new. Should I isolate the washdown pump on a differnt circuit? Thanks.

you've got a problem in the power supply side to the radar,or it's on the ground side...

paralleling the 2 batteries,it combines the amperage available,but,if the wiring is poorly connected,or,the incorrect guage,it will not flow anymore-therefore,combing the batteries makes no difference...
i wold reccomend you have the boat checked out by a qualified individual.i recall you having this problem,you brought this very topic up in another thread...

OK, Thanks.