Back in April 24, i my 2019 Fusion Hybrid with 30K miles was having trouble locking and unlocking the keyless passenger door. and if the car sat idle for 2-3 weeks, it had no interior lights and no power to start. Knowing what i know now, i should have checked for a parasite current draw first, but i replaced the 12v battery and everything was working correctly and my MPG went up roughly 5 MPG. Great. Move ahead to November and i am having trouble once again entering the car via the passenger door. I went back to Autozone while my warranty was still good. They tested it and said nothing is wrong with the battery but needed a charge. I see my 12v goes from just shy of 12v when car is off, then jumps to >14 when i start the car, but the Autozone rep says it may not be always charging that much and my battery is actually discharging while driving. I also see my MPG is a solid 35 MPG and not any better.
I did some research and came to the conclusion the DC DC converter may be faulty and changed it out even though the car only had 30K miles and would be a premature failure. Apparently, you cannot buy a brand new converter, and all on ebay are used ones from salvage yards i gather. . I installed one, and the Internal Combustion Engine (ICE) would not start up. I could go into gear, and the car would not move. I searched just about everything on the internet and not figuring out why the ICE would not kick in. Its like a reset needs to occur after replacing but not finding any such info to confirm. I put the original back in and it started up and drove like it is supposed to. I contacted the ebay seller and he sent me another inverter and it did the same thing. ICE will not fire, but old back in and it works just fine.
Anyone have an idea why two inverters are not lighting off the ICE, or why my 12v is not staying charged?

thanks
Ken

 

If you don't drive it at least 30 miles highway mileage weekly, you should get a charger like Noco Genius 5 or 10 so you can charge it once a month. Additionally buy a bluetooth battery monitor so you can monitor its status over your cellphone.
If you don't park it inside a garage, go solar and install a solar panel, get the biggest possible and install it on top of your cargo cover. Check this thread if you want to go solar, it's so affordable these days, most importantly, install it and forget it. The solar charger will kick in automatically whenever your vehicle is not running.

 

Don't know if this applies here, but if the key FOB is close enough to the vehicle it will prevent the modules in the vehicle network from going into sleep mode and if they don't
it will keep draining power from the 12 volt battery. You might try increasing the distance of the FOB from the vehicle.

Let us know if this helps solve the drain problem, thanks.