Leisure Battery Blues!

Discussion in 'Tech/Mech General' started by juliandavies, Feb 24, 2009.

  1. juliandavies

    juliandavies Read Only Funster

    Dec 12, 2008
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    Crystal Palace, London
    I've been wild camping in London (?!) since Saturday with no mains hook up and am struggling to work out what power my batteries can give me.
    They just seem to be losing power quickly.

    What I know:
    1 - I have 2 Marathon M12V150FT 150 Amp leisure batteries.
    2 - Apparently 12.7V is fully-charged, 12.3V is half charged, 11.8V is dead.
    3 - Batteries should not be run on less than 50% charged.
    4 - The batteries have been fully charged on the mains in the last week.
    5 - After charging, batteries must rest for 4 hours before an accurate reading can be taken.

    Case study:
    Took a reading of 12.53V, ran two 12V lights for one hour (NO other power, even step light off) - went down to 12.41.
    Ran same two lights for another hour, went down to 12.3V.
    Ran the generator for 5 mins just to get them going (up to 12.68).
    Used no power till the following morning - reading of 12.45.

    Concerned that something is wrong.
    Any help appreciated!
    Wildman - are you out there? :Smile:
  2. TJ-RV

    TJ-RV Deleted User

    Two of those batteries wired in parallel give you approx 300 amp hours. Ignoring the 50% rulle occasionally won't hurt, but repeated deep discharge below 50% will reduce their life. So, you essentially have 150 amp hours.

    Is your concern that the batteries won't hold their charge any more? How old are they, and have you seen any degradation? Just trying to figure out which problem we're trying to solve.

    You can expect to see voltage drop as a result of surface charge bleeding off. I wouldn't hope to replace much charge by running the generator for 5 minutes.

    Voltage is a good indicator of the state of charge, but I wouldn't rely on it to determine if your batteries are good. The only ways to do that are:

    1. Use a load tester.

    2. Run a known heavy load for an extended time.

    Which charger/converter do you have? Do you know what its charging characteristics are? A good charger for deep cycle batteries will have 3 stages of charge - bulk, absorption, and float. Re-charging discharged batteries will take several hours.

    If the ability of the batteries to hold their charge has diminished, it's sometimes an indication that they need equalizing. But, unless your charger has an equalizing feature, that's academic. If it does have that feature, I've repeatedly seen significant improvement in the ability of deep cycle batteries to hold their charge following an equalization cycle. (Takes several hours after batteries have been fully charged.)
    Last edited by a moderator: Feb 24, 2009
  3. Douglas

    Douglas Read Only Funster

    Aug 22, 2008
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    South Wales,
    I have seen this kind of thing a few times and before you go thinking the worst try this.

    If your batteries are the refill type check the electrolite level

    If you have a meter measure the voltage from every battery post and then from every battery clamp, if there is any difference the clean the posts and use vasilene on them if they are dry.

    I know its not rocket science but its often the simple things that get missed.

  4. juliandavies

    juliandavies Read Only Funster

    Dec 12, 2008
    Likes Received:
    Crystal Palace, London
    thanks for the detailed reply - although I do now feel like a real idiot!
    - not sure I understand why I have 150 rather than 300 amp hrs?
    I think you're spote on - I dont think they are holding their power anymore. I recently bought the RV so although they look good and were OKd during recent service, they may be as old
    would most garages have a load tester or should I buy one?
    Not sure what sort of charger/converter I have! There is one by the water pump but I figured that was just for the water pump. Would the leisure batteries have a seperate charger?
    Sorry for my ignorance!
  5. Losos

    Losos Read Only Funster

    Feb 17, 2009
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    Suffolk & Czechland
    Just like to add a couple of points :-
    a) As Doug has said "If your batteries are the refill type check the electrolite level" in my experience this often is the cause and is easily remidied.

    b) I would assume from your comment above that your leisure batteries are the originals and if your RV is more than a few years old they have probably had a hard life and may even have been run flat on more than one occassion and this is what starts the decline in 'holding' power.
  6. TJ-RV

    TJ-RV Deleted User

    Delayed response - I spent all day at the hospital with a neighbour.

    The batteries have a stated capacity of approx 150 AH each. Two connected in parallel gives a total of 300 AH. However, the rule of thumb is you shouldn't regularly discharge them more than 50%, so you really have 150 AH to work with.

    I'm on the other side of the Atlantic, and here we can walk into any automotive place and ask them to put a load tester on a battery. I'm sure you could do the same thing, but beware of the shark who just wants to sell you new batteries. Load testers are relatively inexpensive here, but probably hard to justify for a 1-time use.

    I suspect that what you have is a converter that powers all the 12 volt stuff, and the converter doubles as a battery charger. We see lots of folks with converters that are really poor chargers. By that, I mean that they have no means to vary the charge as the batteries come up, and the batteries literally get cooked.

    The suggestions made by others here are worth looking at before you fork out hard-earned cash for new batteries.
    Last edited by a moderator: Feb 25, 2009
  7. Terry

    Terry Funster

    Dec 27, 2007
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    South yorks
    Hi go down to your local spares shop,I am sure they will have a load tester and test the battery's for free in the hope of making a sale :thumb:
    edit also agree with Jaws below
    Last edited: Feb 25, 2009
  8. Jaws

    Jaws Funster Life Member

    Sep 26, 2008
    Likes Received:
    Ummm.. me being me and having worked in the field for a errrrr well a wee while ( :BigGrin: ), I always suspect the test equipement first !

    I would check your meter either agin another one or at least the one you have on another battery..

    The fully charged batteries ( according to the meter used ) were .17v down to start with.
    If you assume this to be an error and they were in fact sitting at the full 12.7v to start with, that would mean the voltage is actually only dropping down to 12.47 after a bit of use.
    I have a pair of sealed leasure batteries in my unit that, from new ( and according to my Fluke ) have been duff from day one !
    Personally I would not be too paranoid about it..
    As others have said, it aint good to deep discharge a battery but doing it once should not harm them.
    I would put the meter away and just see how long they last until the telly goes off ! :Smile:

    Not terribly scientific I know but at leat you will know the true state of play

    Word of warning re load testers..
    Many new style batteries are of the gel type.
    Put one of those things on it for a few seconds and tis off to buy a new battery or two.. They REALLY mess them up !( Go to any of the bigger battery makers sites and you will find this info buried away on all of them.. They often do not splash the info out loud as they would much rather you buy a new battery !!
    Last edited: Feb 25, 2009
  9. TJ-RV

    TJ-RV Deleted User

    That's the best advice so far.

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