I think I’ll stick with my Midtronics conductive tester; good, accurate results 
on the health of my golf-cart and start batteries, it only takes a minute, and 
no chance of starting things on fire…   :^)

Fred Street -- Minneapolis
S/V Oceanis (1979 C&C Landfall 38) -- on the hard in Bayfield, WI   :^(

> On Feb 7, 2017, at 4:52 PM, Josh Muckley via CnC-List <cnc-list@cnc-list.com> 
> wrote:
> 
> There is no need to go full discharge.  The voltage and capacity properties 
> of a lead-acid battery have a near linear relationship so a 50% discharge is 
> fine for testing.  That should be 11.6v.  All of this is just a comparison.  
> A brand new battery might show +/- 10% of the labeled rating.  That doesn't 
> mean that you got a good or bad battery.  It's just an indication of how 
> difficult it is to accurately measure the capacity.  Typically batteries are 
> only considered at their end of life until they only test at 50% of original 
> labeled capacity.  Capacity tests really are most powerful as a trending and 
> comparison measurement rather than a go/no-go.  I've successfully used 100Ah 
> batteries that measured at only 7Ah.  I know they are junk but keep them 
> around for various workbench projects.  I've even used them to successfully 
> start my spare marine diesel sitting in the garage.
> 
> Josh Muckley
> S/V Sea Hawk
> 1989 C&C 37+
> Solomons, MD

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