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flicks
flicks

Posted: Fri Jan 07, 2011 7:42pm

Post Subject: Battery blues

Hi Tony. I wonder if you could offer me a bit of advice please. We went to visit our little narrowboat a few weeks ago only to discover the winter chill had flattened our batteries. We had no chance of starting the engine and the internal lights although operative were very dim. We purchased a decent marine battery charger and got the batteries home. We went back to the boat this week and installed the freshly charged batteries but they were still dead as dodos. Further charging found that only a few of the cells were bubbling which says to me that the batteries have been totally destroyed. So, it's time to buy some new ones and that's where the real problem comes in. I have established that these are two 100Ah leisure batteries but I am confused as to the way they are wired. The batteries sit side by side in the battery box each with it's own isolating switch. One of the batteries has two wires running from the negative terminal and the other only has one. Both of the batteries have only one wire running from the positive terminal. I am wondering why one of the batteries has two negative wires. Is this to supply a total of 24v when starting would you say? I assumed that one battery would be for starting purposes and the other for lighting etc but this doesn't seem to be the case. I just need to make sure that I purchase the correct batteries for the job. Sadly the existing batteries are old and have no labels on them. Any advice would be hugely appreciated. Many thanks.

Tony-B
Tony-B

Posted: Fri Jan 07, 2011 9:44pm

Post Subject: Battery blues

Usual caveats about not being able to inspect the boat. If you really do only have two batteries and both have separate master switches I think one is likely to be the engine start battery and one the domestic battery. With just two batteries I think you must have some form of split charging system and for this to work the negatives of both batteries need connecting together so I would expect the engine battery to have one negative lead running to the engien block or starter case and another to the domestic battery negative. The domestic battery negative would then have an additional negative cable running back to the fuse box or wherever the main domestic negative junction plate/bus bar is located. That however puts two negative cables on both batteries. It is possible that the joined negative leads are on the engine but that is unconventional, but it may explain the two plus one lead arrangement. If you are saying that both batteries supply all the boat (both starting and domestic load) then the positive of one battery should be connected to the positive of the other one and ditto the negatives. There should only be one master switch and the supply leads should be attached positive to one battery and negative to the other (actually they could both be connected to one battery but its not best practise). Now unless you care to email some digi-pics to Tony@TB-Training.co.uk of the batteries and where the wires run to I stand no chance of saying more - even then I may not be able to sort it out. AS far as the batteries go there things are far easier. Nowadays it is easy to get Leisure batteries that state they can be used for starting or supplying the domestic load so just look out for dual purpose batteries and although they may not give you the absolute maximum life they will do the job for you. It will not be worth spending any more until you sort out exactly what the electrical system is up to. Tony Brooks

flicks
flicks

Posted: Sat Jan 08, 2011 9:38am

Post Subject: Battery blues

Many thanks Tony. We just got caught out totally by the early spell of freezing weather this year. A newbie error for sure but now it's going to cost us a couple of hundred quid we can all rest assured that won't be happening again! There is certainly only one of the batteries which is for domestic purposes as when the non domestic battry is isolated the lights etc still remain on. The reason I thought that maybe they worked as a team for starting purposes was because I assumed, (probably wrongly), that one 100Ah leisure battery would not contain enough power to crank over an engine. It is only a Lister SR2 though so I guess that could well be the case. As we need to replace the batteries we will do so and if we encounter any further issues I shall get some picturesd and e.mailo them to you. Once again thanks for your help. Hugely appreciated.

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