Have searched but was unable to find:
2 dash 12v outlets - Side by side - Which one is the engine batteries and which is house? :facepalm:
Pick up one (or two) of those cheap lighter socket voltmeters. They are available in many auto parts stores, or online. Plug it in one of the outlets, and crank the engine. If the voltage drops, that is the start battery outlet. If it doesn't, you are in the house battery outlet.
Two plug-in voltmeters are nice to have. Leave them in the lighter sockets all the time for a quick comparative check of battery bank condition.
Amazon.com: LCD Cigarette Lighter Voltage Digital Panel Meter Volt Voltmeter... (https://www.amazon.com/Cigarette-Lighter-Voltage-Digital-Voltmeter/dp/B00UCEAKYU/ref=pd_sim_263_4?_encoding=UTF8&pd_rd_i=B00UCEAKYU&pd_rd_r=90d03c08-c13a-11e8-811e-95119e74d328&pd_rd_w=2ebAk&pd_rd_wg=zxr0i&pf_rd_i=desktop-dp-sims&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=18bb0b78-4200-49b9-ac91-f141d61a1780&pf_rd_r=D2N0V0K8X3EP9VDS0CR1&pf_rd_s=desktop-dp-sims&pf_rd_t=40701&psc=1&refRID=D2N0V0K8X3EP9VDS0CR1)
I use a pair of these.
Car Charger 5V/3.1A Quick Charge Dual USB Port Cigarette Lighter Adapter New... (https://www.ebay.com%2Fulk%2Fitm%2F113000838738)
They have two USB ports and show voltage until something is plugged into one or both ports, then show usb current. Pretty cool in a nerdy way.
......OR......turn on the ignition switch and watch the dash volt gauge. Push in the cigarette lighter and if the gauge moves slightly that's the start battery plug.
Scott, one of mine has a rubber cap. Pretty sure that one is the on all the time one. Or it is the other way around.
If you are getting a 12v charger for a laptop be sure to get one that is certified for quick charge QC 2.0 or QC 3.0.