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Posted: Mon Dec 21, 2009 3:43pm

Post Subject: Domestic batteries

I am a member of a shared ownership syndicate with a 57' narrowboat. The boat was launched in 2006 and is in almost constant use apart from 4 weeks maintenance each year. Over the past year or so it has suffered failure of individual batteries in the 6 x 12V lead-acid domestic battery bank. These batteries have been replaced individually as required. My first question: is it best practice to change all batteries as soon as one fails? Assuming the answer is 'yes' then ought we to consider upgrading to more robust batteries and if so would you suggest deep-cycle batteries? The rating of the existing batteries is 110AH although some have been replaced with 95AH and I believe the alternator is rated at 150A. Would any alterations be required if we were able to upgrade?


Posted: Mon Dec 21, 2009 5:24pm

Post Subject: Domestic batteries

Dear Kevin, accepted practise is to replace batteries in whole banks BUT that probably has more to do with the possibility that one faulty battery can cause damage to the rest. If you replace single batteries AND regularly test and check the older batteries it should be OK, but most people do not bother and with sealed batteries probably do not have the equipment. Although it is possible to test sealed batteries with a voltmeter it would be all but impossible with the use you describe because it involves leaving them standing, fully charged for many hours. I do not believe anyone can advise you on your best way forward (although they may appear to) without far more information and on a shared boat that information would be all but impossible to come by. I would need to see a realistic power audit for each user for each month of the year and also the minimum and maximum engine running hours per day alongside each power audit. I would also need to see the battery voltage before the engine is started first thing each morning and again one hour after shutdown at night for each user and times of year. Only then could I start to advise. My feeling is that you are probably killing the batteries with sulphation (in common with probably 70% of other boaters without long term 24/7 charging facilities) and that two to three years life is to be expected. If you can be absolutely sure that it is possible to get the batteries 100% charged each day AND never discharge them to below 12.3 volts then fitting expensive batteries may make economic sense, but if you can not then I feel cheaper, wet open cell batteries of so called deep cycle. leisure or dual purpose design will probably be the most cost effective. You also need to be 100% sure the charging system is not causing any voltdrop on the cables and the batteries are correctly connected. A quick "guesstimate" suggests that your main charging cables (both pos & neg should have conductors of about 40sq mm. They should also be attached to the batteries at opposite ends of the bank but without knowing far more about your system I can not say too much more I would advise all the owners to study and understand the content of Tony Brooks

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