I haven’t had access to grid power in over 10 years and am pretty familiar with this stuff as part of day to day life. I do now have solar. Really don’t think me and everyone else I know have been getting this consistently “lucky” for this long across such a wide range of devices. The 11-15v a nominal 12v battery system normally experiences is not a huge amount of fluctuation, and I have yet to encounter a 12v device that couldn’t take it. On the contrary, I’ve tried much dumber stuff and gotten away with it. There’s a 9v piano keyboard and a 19v computer monitor wired straight into that same battery. The only time I’ve actually killed something is by reversing polarity. Voltage too low=won’t turn on, voltage too high=gets hot, and all these years of wiring up random scavengings to see what happens have taught me most gear is surprisingly tolerant/resilient