In my time, I have seen many fires caused by inadequate wiring, fusing and poor installation... both with isolators and without. When I see a secondary battery without a fuse on the charge wire I cringe. Many people feel it's not necessary but I disagree. I've been in 2 car fires caused by sub-par wiring, both with single batts, the 2nd I was test driving a Mercedes on the freeway. It's amazing how fast you can't see due to smoke and you can't open the windows. Also, many of the dual battery kits I've seen from inexpensive to very expensive do not have adequate gauge wiring to handle high-current situations, are set up to use the chasis of the vehicle as the return which makes the system not truly isolated and negates the peformance of wire above 4awg.
I've never needed 24V in my vehicle and I willing to bet most people don't either since we have 12V charging systems on most vehicles. I wasn't aware of a system that allows you to series the batts, I've only seen a system that allows you to parallel them. How much capacity does the average person need? I bet the average person doesn't know.
All power to run accessories come from the charging system and no system is going to change that. You can increase reserve time with a dual batt system but the butcher's bill will still need to be paid and average power over time really doesn't change with a dual batt system. That butcher's bill can be quite taxing when it comes due since now the charging system has an additional load.
As you'll note, I don't speak in absolutes. I use words like "most" and "opinion". I've been around 12V for many years and was once highly regarded, I believe I've seen more than hundreds of examples of 12V systems both well executed and not... I mean if I were going to lie about being an expert about something, I'd pick something cooler than 12V systems... I'd pick cowboy or fireman. I feel that I've earned the right to express my opininion as an expert on such matters and acknowledge that there is a time and place but the advantages of a dual batt system do not apply to most people... and if my alternative is installed improperly there's no fire... it just won't work and won't be an additional load on the alternator either. I've installed many dual batt systems in my time, I'd dare say perhaps more than anyone on here. In the days before there were kits with dual batt monitors and "all" the wiring you'll need. The right way IMO, is at least 2 AWG wire, both the power wire and ground wire isolated and a bigger alternator. Short of improving all the pathways and increasing the capacity of the charging system, a dual batt system will not reach it's true potential. I really don't see anyone doing this so I'm going to be outspoken about it.
As my final 2 cents I'd like to point out that I carefully selected the word "alternative" and that's my story about the truth. You'll be happy to know we'll have a reseller program with master carton quanties of 10. When can I expect a PO Kurt?
