Analysing bat­ter­ies

Canal Boat - - Back Cabin: Experts -

QI have just pur­chased a CTEK bat­tery anal­yser to check my leisure bat­ter­ies as we’ve de­vel­oped bat­tery prob­lems. All of my bat­ter­ies are 110 Ah (Amp hours) and 680 CCA (Cold Crank­ing Am­per­age). I fully charged all three be­fore car­ry­ing out the test. The anal­yser told me one re­quired re­plac­ing be­cause it was show­ing 575 CCA. How low can the CCA go be­fore it’s classed as use­less? It would be good to know be­cause, by us­ing the anal­yser, I would be able to change a bat­tery be­fore it starts giv­ing prob­lems. A CLARKE

ATONY REPLIES… The good news is that it ap­pears not to be a high rate dis­charge tester, the bad news is that Cold Crank­ing Am­per­age (CCA) is re­lated to en­gine start­ing, not long dis­charges at a low rate that boat’s do­mes­tic bat­ter­ies are sub­ject to un­less a large in­verter is be­ing used. Add to that the fact that such testers’ al­go­rithms dif­fer from maker to maker and tend to give dif­fer­ent re­sults. One author­ity even says that a start­ing bat­tery with a low CCA can give sev­eral more months or years more use, prob­a­bly more so with the long slow dis­charges boat bat­ter­ies get.

I have no idea how low the CCA can go be­fore the bat­tery is con­sid­ered to need re­plac­ing be­cause, for a do­mes­tic bat­tery use, it’s a pretty mean­ing­less fig­ure. When the Ah ca­pac­ity falls to 50% of the orig­i­nal or when a cell starts to fail, the bat­tery needs re­plac­ing.

Un­less you fully charge the bat­ter­ies at least once a week (and I do not mean when an amp hour count­ing me­ter says they are at 100%) then most boaters will sul­phate their bat­ter­ies so they slowly lose ca­pac­ity. You can sul­phate a bat­tery within weeks but most take far longer than that.

Even if you do charge your bat­tery to 100% at least once a week, stan­dard ‘leisure’ type bat­ter­ies have a very lim­ited cyclic life (typ­i­cally be­tween 150 and 300 cy­cles) and once that is used up are likely to de­velop short circuits within a cell or cells.

I note the anal­yser stresses that you need to fully charge any ‘low’ bat­ter­ies be­fore re-test­ing them but makes no men­tion of let­ting them stand overnight to dis­si­pate the sur­face charge and al­low time for any short­ing cell to dis­charge. I think this omis­sion could lead to false ‘okay’ read­ings. Check with CTEK who know the al­go­rithm their tester uses.

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