Josh is correct in saying that the best predictor of the capacity of a battery is the weight… the more lead there is in the plates, the more energy it can store.
“Amp-Hours” is basically an automotive test. Ditto for “reserve capacity”. They tell you for how long the battery will supply electricity to keep your car running if the charging system fails. (It used to be that a car would draw 20 or 25 amps (I’ve been retired too long and can’t recall the exact rate) so the reserve capacity (in minutes) is how long the battery will supply that amperage before the voltage gets so low that the car’s ignition no longer works.) One problem with measuring Amp-hours is that the number depends on the amps being delivered. Amp-Hours is the product of the current being drawn and the time before the battery voltage drops below a certain minimum. The problem being that the depletion of the battery is not linear – a battery delivering 5 amps will last quite a bit more than twice as long as a battery delivering 10 amps, and way more than 4 times as long as one delivering 20 amps. So the amp-hour rating on the label is an indicator of capacity, but YMMV and depend on the actual usage for the 12 volt systems on your boat. On Imzadi the amps being used in normal daytime operation varies from under 2 amps to about 5 depending on whether the fridge compressor is running or not, and whether the stereo is on. For typical cruising days, amp-hour consumption is in the neighborhood of 75 AH in 24 hours – more than half of that for the fridge. If you can actually see the specs of the batteries you are considering buy the heaviest of the alternatives. And, BTW, the Link battery monitor on Imzadi has an algorithm built in that updates the total capacity of the battery bank over time as you repeatedly “sync” the batteries to indicate that they are fully charged. I think it does it based on the amount of current that is put back into the battery during charging, but I’d need too refresh my memory before asseting that to be a fact. Rick Brass Washington, NC From: CnC-List [mailto:[email protected]] On Behalf Of Josh Muckley via CnC-List Sent: Monday, January 27, 2020 6:43 PM To: C&C List <[email protected]> Cc: Josh Muckley <[email protected]> Subject: Re: Stus-List Battery Amp Hours? Edd, I have tested A-Hrs and recommend that everyone do so in some manner before deciding that their battery needs to be replaced. https://youtu.be/vbsFt5aaLOU https://youtu.be/wfx-i7_AKw4 https://youtu.be/PvT-I4WtgPU The best metric when buying batteries is their weight not so much their A-Hrs. Josh Muckley S/V Sea Hawk 1989 C&C 37+ Solomons, MD On Mon, Jan 27, 2020, 4:15 PM Edd Schillay via CnC-List <[email protected] <mailto:[email protected]> > wrote: Listers, Hope everyone had a great New Years. So when you buy a battery, it’s pretty clear from the label what it’s Amp Hour rating is — so how does one actually verify that information? Is there any way to test your battery’s actual Amp Hours when they are either new or used for some time (but fully charged)?? All the best, Edd Edd M. Schillay Captain of the Starship Enterprise C&C 37+ | Sail No: NCC-1701-B Venice Yacht Club | Venice Island, FL Starship Enterprise's Captain's Log <http://enterpriseb.blogspot.com/> _______________________________________________ Thanks everyone for supporting this list with your contributions. Each and every one is greatly appreciated. If you want to support the list - use PayPal to send contribution -- https://www.paypal.me/stumurray
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