ok i just bought 2 1100 something cca starting batterys for a house bank for my espar and qc and plan to add a 1000 watt cobra inverter...what i need to know is whats the rate of hours you get per cca or at least whats the fourmla for it. please and thank you
Moot and RLENT covered it. And to help you save on the cost of aspirin, I'll use no math here.
But, you said it yourself... you bought two
starting batteries (cranking batteries) for a
house bank (deep cycle usage).
There is no formula for converting CCA into Reserve Time (rate of hours, or amp hours). CCA is a few seconds of a big fat hairy jolt of electricity used to crank the starter motor to start the engine. Starting batteries are designed to supply a lot of amps all in one whack, but they don't work very well at all at supplying the lower amp draws for extended periods as are necessary for a house bank.
Marine batteries, like the Everstart Maxx at Wal Mart, are marketed as "deep cycle" batteries for marine use, but they aren't deep cycle at all. They're merely cranking batteries with slightly thicker plates that make them deep-er cycle than a standard cranking battery. They are a "hybrid" between starting and deep cycle. They are made for the relatively low amp draw of a trolling motor (which is the same type of draw as an Espar heater, by the way).
I've got four of the Everstart Maxx batteries in my van, and I thoroughly abuse them with a laptop with 3 external hard drives, florescent lights, Espar heater and a Microfridge (fridge, frost-free freezer and a microwave), as well as a printer/scanner/copier.
You will see batteries listed with CCA, MCA and CA.
CCA = number of amps a battery can supply for 30 seconds at zero degrees F. That's so you'll know how many amps you have in the dead of winter, 'cause the colder it is out there the less amps a battery will have.
MCA = number of amps a battery can supply for 30 seconds at 32° F. Who goes out in a bass boat when it's below freezing? That's why they use 32° to rate marine batteries.
CA = number of amps a battery can supply for 30 seconds at 80° F. Mostly used for simple comparisons with car and truck batteries, but it does have critical implications in some heavy machinery applications and in some emergency vehicle applications.
None of these cranking amps numbers have anything to do with how many amp hours a battery has or how many minutes of Reserve Time it might have. A high-end $750 solid lead plate deep cycle battery might have 1100 Cold Cranking Amps and have 220 amp hours of capacity with 390 Reserve Minutes, whereas a $75 starting battery from Auto Zone might have the same 1100 Cold Cranking Amps, but might have 40 amp hours and a Reserve Capacity of 35 minutes before the battery is drained dry.
But the real difference comes with what is known as Reduced Capacity. Every time you discharge and recharge a battery (known as a cycle), some of its original capacity is lost (that's why batteries eventually wear out). The deeper you discharge the battery, the quicker it will wear out due to lost capacity.
Let's say you only discharge them down to 50% and then fully recharge them up to at least 95%, and let's call that one cycle. With true deep cycle batteries, very little of the original capacity is lost with each cycle. With marine hybrids, a few percent is lost with each cycle. With cranking batteries, a significant amount of capacity is lost with each 50% cycle, as cranking batteries are not designed to be drawn down anywhere near 50%, but rather 10-20% and then be recharged in a matter of minutes by the alternator.
In your car, truck or van, if you leave a dome light on overnight and run the battery down, you've probably cut the lifespan of that battery in half, and the total capacity by 25% or more. That means you might still be able to get 1100 CCA out of it for starting, but only for 15 or 20 seconds, not for 30 seconds. Leave the dome light on 4 or 5 times and you'll replace that battery after a year or two instead of after 5 or 6 years.
Your starting batteries may, in fact, be marine hybrids, and if that's the case, chances are they'll be fine for the Espar and limited inverter use. If they are truly starting batteries, with the thin plates needed strictly for starting, be prepared to replace them in about 6-8 months, 12 if you're lucky and always flip the switch on the inverter to actually turn if off when you're not using it. Even if you have nothing plugged into the inverter, if it's turned on, the inverter itself will draw anywhere from half an amp to 1.5 amps all on it's own. A one-amp draw will run a car battery dead overnight, and it's that kind of draw that kills a starting battery and severely shortens its lifespan.
So, the question is, exactly what brand and model number are those batteries, and what are all of the numbers listed on the case?
OK, that's two questions. Math. My bad.
