Len, there is no free lunch... (i.e. if you do it cheap or quickly, the results will be questionable).
Joe’s way is probably the best way to do it, provided that you can maintain a steady 20 A current through the load and that you can stop the discharge at the particular voltage level (you have to watch it). I would suggest looking up this web site: http://www.pbase.com/mainecruising/boat_projects and specifically, this article: http://www.pbase.com/mainecruising/battery_state_of_charge. This should give you plenty of advice. You would also find that the battery monitors, usually, just measure the current flowing out of the battery (batteries) and potentially, the voltage. So they might tell you how much charge you have used, but they won’t tell you the SoC of the battery. good luck Marek From: Della Barba, Joe via CnC-List Sent: Tuesday, February 7, 2017 10:16 To: cnc-list@cnc-list.com Cc: Della Barba, Joe Subject: Re: Stus-List Battery test Easy cheap way. If you have accurate volt and amp meters, a 20 amp (or near enough) load applied for enough time to drain the batteries 50%*. You should see 12.2 for wet cells and 12.3 or so for gel/agm. Light loads like 1-5 amps and heavy loads like 50-100 amps both will be inaccurate because of Peukert’s law. This law deals with the fact that a 100 AH battery can supply 100 amps for 1 hour or 1 amp for 100 hours in theory, but in practice 1 amp will last longer than 100 hours and 100 amps won’t make the full hour. 20 amps is a good value for these tests. * (AH capacity of batteries/load in amps) /2 = time in hours for 50% discharge From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Russ & Melody via CnC-List Sent: Tuesday, February 07, 2017 00:41 To: cnc-list@cnc-list.com Cc: Russ & Melody <russ...@telus.net> Subject: Re: Stus-List Battery test Hi Len, If you're 100 percent full and have a coffee in your hand, may I suggest some advice from Bobby... and words I live by. Don't warry. Be Happy. Cheers, Russ Sweet 35 mk-1 At 07:28 PM 06/02/2017, you wrote: I think the CBA would work well so far from the little reading I have done. I have four 6 volt deep cycle batteries for my house bank and a Link monitor. I also have a simple analogue load tester. The problem is the solar panel masks any shortfall in the bank by fully charging usually before I make coffee in the morning. The house bank isn't quite as full on a rainy day and everything works but I would like to know how well. I probably should just leave it alone but if the bank is 100% charged but at 50% amp hour capacity I want to know. Len
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