Discussing different views with the boss

Hows it goin, not too sure if this is on topic enough but it is definitely car audio related. I work for a car audio shop and have been for the last 3 years, I live and breath car audio. Anyway I have been getting into a few altercations with my employer over differences in opinions when it comes to adding larger systems to cars. Now, (let's just call him Dave) Dave isn't unintelligent. He's very intelligent but he has a very ingrained view of how systems work and how they should be designed. We dont get many big systems through the shop (>2000wrms) but when we do his solution to aid the charging system is to add a second battery to the car to supply the new system and seperate that from the rest of the car by putting a DC-DC charger inbetween the secondry battery and the existing charging system. This is connected using a 8 guage cable to the boot where the second battery is. This charger activates when one of the batterys (I forget which one) reaches a certain voltage. Now we did this to a '15 WRX running E85 lately. The execution of the design by our other installer was perfect. Everything done to a really high standard. The customer has come back absolutely fuming. Apparently he'd been driving along and the car has spazzed out and started running really rough, maybe gone into some sort of limp mode and smoke was coming from under the bonnet. Turns out the fuse (which was located under the E85 fuel line) had started melting and was all sorts of burnt up. He was wizzed, and rightly so. I was the only one at the shop, the installer for the job and the boss was out at the time so I sorted him out, calmed him down and reverted his car back to stock by taking the fuse holders and dc-dc charger out. I then took the battery negative off and left it for a few minutes and when i put it back on the fault lights on the instrume t cluster were gone and the car had returned to a slightly less doodiety idle. He was going to go to his tuner to sort that out and I asked him to give us a call to let us know how it went and also so we can sort out a fix for the issue. We haven't heard from him since. And yet even though this has happened he remains adament that there is no issue with the design and that the idiot end user should have known that the needs to periodically and manually charge his system if he is going to bump it loud. I actually tried to explain to him that it's not the battery that runs the electronics when the car is running but the alternator but this was met by him squaring up to me and literally swearing at me, (in front of a customer mind you) telling me basically that I dont know doodie and should shut up. I want to be able to suggest instead of doing it that way, that for larger systems that need more current we instead replace the alternator and main power cables (Big 3) with larger current handling items. This is apparently unheard of and is a load of crap and have you ever done this before and you dont know doodie about doodie. Basically my question is how do I explain to him my point of view without getting railed on about it and how do I get him to see a different point of view? The other installer is no help, he's a yes man through and through and has no opinion of his own. It's not just this issue either. He also believes that using larger cables is not only unhelpful, its actually detrimental to the system because of what is known as the skinning effect which is the propensity for current to travel on the outside of the cable and so the extra thickness of the cable is wasted. Which I found out after researching is actually true however only for AC voltage. I also brought this up with him but again was met with furious resistance. Just know that thes are just examples and in no way reflect his whole character, apart from things like this he's actually a fairly decent guy. So what the love sould I do?