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2008 Element EX AWD TRP
2,948 Posts
From a hypothetical point of view, the run time is the ampere hour rating of the battery divided by the load current.

The load depends, not on the models of your equipment, but on how loud you crank it. There is no spec on maximum input load current on the page you reference. The spec you reference says the DVD player has its own amplifiers. If the DVD player were wired directly to the battery, assuming that the amps are 50% efficient, it would draw an max current of (22W x 4 x2)/12V=14A. (Personally, I think you'd have to be a sadist to crank up the output to this level, which using good speakers, would represent 2-3W of acoustic power - enough to permanently damage your hearing- while watching a 7" LCD image.)

Anyway, continuing this hypothetical discussing, the Reserve Capacity Minutes is how long a battery will power a 25A load before the output voltage drops to 10.5V. If you can find this spec for the Honda OEM battery, you could estimate that the DVD player alone would work for about twice the RCM.

Since we don't have hypothetical vehicles, from a practical viewpoint, why don't you try it in your driveway? Use a digital voltmeter across the battery, measure how long it takes for the terminal voltage drops to 10.5V, and call that your max run time. (Keep a battery charger handy:lol:.)

Finally, adding a capacitor as a power buffer might reduce ignition noise, and may improve the dynamic response of the audio system; it won't extend run time. Capacitors are "lossy" (self-discharge). Adding one will decrease your run time.
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