There are days when I clearly don't know what I am doing. The past 24 hours has been that kind of day. At night I sleep with a CPAP as I have sleep apnea. A CPAP is a device that provided Continuous Positive Air Pressure, keeps me from snoring and thusly I no longer stop breathing while I sleep. Thanks to this device I may have a few more days in this life to write these stupid words for you to read. The problem is that my CPAP plugs into the wall in the bedroom and we are going camping which, typically, doesn't have an outlet. So, for the past several weeks (just feels like months) I have been researching alternative power methods. As it turns out I can run the CPAP off of a 12 volt battery.. so I researched battery alternatives. Goal Zero makes some very cool power devices but they seem quite expensive and take a long time to recharge, and they don't hold a lot of amp hours. Amp hours are what I desire. Having lived a 12 volt life when we lived on our boat I am familiar, just a bit, with what is called a 'house battery', so I figured I could just hook up a second battery in the car and charge it with the car's alternator..it's what we did on the boat. Boy oh boy does it ever take a lot of hard thinking to get this worked out right. After many hours of study and hours and hours of searching on the internet for things that will work I made my purchases and started in on actually installing the system in the car. Now this is a scary thing to do because we just bought this car, a 2017 Subaru Outback, and I would sure hate to screw it up, blow out the electronics or burn it to the ground. But the electrical Gods have smiled down on me long long ago and gave me an older brother who knows all about this stuff. Unfortunately he is Illinois, and I am not. So I have been bugging him with phone calls and send texts and pix so he can help guide me through this minefield of electrical bulls**t that I don't understand. So here is what I got. From the primary battery that Subaru put in the car the red wire has a 100 amp ANL Fuse (what ever ANL means) and the line runs through the firewall, through the center console and into the back seat to a Voltage Sensitive Relay Battery Isolator Thing to another 100 amp ANL Fuse and to the red post on the house battery..everything is grounded through the black wire as per instructions from the relay and from my brother. Coming off the battery is a 12 volt outlet which I can plug my CPAP into. The battery I got has 100 amp hours and I figure I can get a few night sleep on this battery before I even have to start the car... this is a good thing. Over all the installation was an interesting process.. I made several mistakes, a few sparks and relocated the battery a few times, however I did not get electrocuted and there was very little blood. In the end I learned a few things that will likely stick with me for along time, like disconnect the ground wire before you do anything. . .and. . . when in doubt, call your brother. Thanks, Dan.