With my 80Ah battery I go 24 hours max between charge cycles. At this level I'm pushing the battery hard and lose some service life- perhaps 20% based on much personal experience with this battery/vehicle combo. I know the expected battery service life and battery cost so I can break it down into daily figures. My battery would last 5 years without the cams but only 4 years with them, and my battery costs $120 so normally $24 per year, and now $30 per year factoring in the 20% loss of life. Divide the $30 by 365 days and
it costs me $0.82 per day in power to run my cam, which I feel is quite reasonable for the peace of mind it gives me.
I've claimed a lower figure here on DCT in the past, but 4 years ago my battery cost just under $80; the $120 is accurate for today so the higher daily cost now.
These are my actual real-life results, mid-grade LA battery, moderate climate, 5.8L gas V8 engine so a fairly high starter load. Drive (or run at fast idle) 20 minutes or more daily. Usually twice a day. Always starts with no noticeable drop in starter speed or strength. Never measured voltages; all I know is that it works and my figures are accurate.
As of today, the best safe-for-use-in-cars battery technology at a reasonable price is LiFePO4, and hefty-sized batteries are common and comparably cheap when you consider they can be very deeply discharged with almost no voltage drop, moreso than any LA or AGM types. Shopping carefully for the good stuff, around $400+ will get you a 100A battery measured as actual usable capacity. That will give you 5+ days recording time and around 3000 charge cycles before significant capacity loss. It needs a specialized MPPT charge controller, but charges fast and considering the lifetime you get from it is likely the cheapest way to go. Only the high initial investment makes this tough to do. Check out
LINK HERE to Will Prowse on YouTube, he's the sharpest around on LiFePO4 battery technology. Some of his older vids relate directly to RV 12V charging, most of his new stuff is solar powered at higher voltages but you'll see how it's done in his vids.
Phil