Forums » Ask a Question

Use this forum to post your questions to our experts – you need to be logged on to do it (you can register here ), then scroll down to the bottom of this page and click the blue Post Thread words

If you can help answer the question, feel free to post a reply – you need to be logged on to do it (you can register here ), then hit the reply button on the thread.

 

To go back to the experts page click here>>

AuthorMessage
Robmarkham
Robmarkham

Posted: Sat May 06, 2017 7:11pm

Post Subject: Leisure Batteries

After a days travelling the charge in my leisure is 14.8 but as soon as i turn the engine off, the charge drops very quickly even though I'm not using any power apart from the inventor. Does this mean that i will have to change all 4 of my leisure batteries

Tony-B
Tony-B

Posted: Sun May 07, 2017 9:48am

Post Subject: Leisure Batteries

Unfortunately there are few hard facts or readings to base my reply upon so all I can do is to offer a number of possibilities so you can make the final diagnosis. The 14.8V reading when the alternator is running plus the "a days travelling" suggests the batteries are probably well charged BUT if a heavy electrical load was running during this time they may not be as well charged as you think. Although they may be well charged there I have no way of assessing their present capacity, they may now only have a fraction of their original capacity so they would discharge quickly. You say that you only have the inverter running but what is it powering? If its an electric kettle, iron, hair dryers and such like it is likely to be drawing between 250 and 300 amps from the battery. This would cause the battery voltage to fall fairly fast. Is this an inverter-charger (combi-unit) or do you have a separate mains battery charger. If so are you sure the battery charger is turned OFF. If not it will be flattening the batteries whilst trying to charge them. Do the batteries have an internal short circuit that prevents them fully charging and then discharges them without any outside help? As you do not mention a rotten egg smell around the batteries, mysteries tarnishing of polished copper and brass, or a battery or batteries bubbling more than the rest and getting hot when being charged together with the 14.8 volts it suggest you probably do not have any shorted cells. A fully charged battery will give a rested off load voltage reading of around 12.75 volts while the 14.8 volts is the alternator’s regulated charging voltage. Within a very few minutes of turning the engine off I would expect the voltage to drop to around 12.75 volts. This is normal. From that point onwards the rate of voltage drop will be proportional to the electrical load AND to the amount of lost of battery capacity. With “typical” electrical loads and batteries in fair condition I would hope the system is well enough specified for the voltage to still be above about 12.2 volts the following morning. If it is not you either have an excessive demand for the size of the bank or the batteries have lost capacity. Batteries lose capacity by a process known as sulphation that is brought about by leaving batteries only partially charged and not recharging them quickly of well enough. If the ends of the batteries are bowed out it tends to indicate excess sulphation. If this is the problem then a new bank of batteries and learning how to look after them better so you do not ruin the new set will be the answer. If there are signs of internal cell short circuits and the batteries are less than about two years old it probably indicates that you have been over discharging them. To optimise the battery life try to never let their rested off load voltage fall below 12.2 volts. At that point recharge them fully. Unfortunately without an ammeter it is difficult to know when to stop charging so many boaters never fully charge their batteries from the alternator. It can take well over 8 hours to achieve and may even put you outside CaRT’s “don’t run engines unless moving between 8pm and 8am” condition. I suspect you will need to come back and ask for clarification. Please feel free to do so.

Robmarkham
Robmarkham

Posted: Sun May 07, 2017 9:04pm

Post Subject: Leisure Batteries

Thank you, Tony, for your full reply. I must admit I didn't give much info on my question. I have a good auto charger built into the boat facilities which I turn on when I'm moored with power supply. I turn it off when I have the engine running. i have left it connected throughout the winter so as to keep the batteries fully charged. The 4 x 110 leisure batteries were in the boat when I bought it last July so I'm not sure how old they are but I don't think they are too old. It seems to me that one of the four is the problem. It has a reading of 9.5 whereas the others have a 12.60 charge. Only recently ,whilst we were out for a week, did we notice any problem. I have noticed since returning to base and plugging in the power supply that there has started to be a "rotten eggs" smell. 2 of the batteries seem to be bubbling. I think, because one of the batteries is not charging, it is drawing from the others and the battery charger is staying on all th time. I hope that by changing the duff one, that they will all start to charge at the same rate and retain the charge after cruising. Sorry for being so basic with my descriptions.

Tony-B
Tony-B

Posted: Mon May 08, 2017 8:44am

Post Subject: Leisure Batteries

Thanks for the added info and from that I can make more definitive comments. The battery that reads 9.5 is almost certain to have a shorting cell in it so needs replacing. it is all but certain that this is one of the bubbling batteries. If another battery or cell(s) within a battery is bubbling far more than the others it also indicates an internal short circuit. I will answer your original question later but first I need to explain more about what is going on. The charging current that flows through a battery is proportional to the difference between the battery voltage and the charging voltage so the battery showing 9.5 volts draws a far greater current than the other batteries. This reduces the current available to the other batteries and probably reduces the charging voltage because of the high charging load it imposes on the alternator or charger. This "fools" the charger into thinking the batteries are not fully charged so it never steps down to its reduced float/maintenance voltage. Not only that but when charging stops the other batteries will try be bale to try to charge the 9.5 volt battery so they discharge far faster than they would do normally. If we put this into your original question and my answer we can see that the voltage would drop form 14.8 to less than 12.7 all but instantly but would continue dropping at a faster than normal rate until the bank was flat. Remember I told you that if batteries are left in a discharged state they sulphate and lose capacity. I also said that the deeper you discharge them the more of their cyclic life you use up. Your battery problem is making both things worse because you can now never fully charge the bank and they are discharging themselves to an unacceptable degree. Now the original question, do you need to change all four batteries? Best commercial practice is to say yes but that is to protect a professional's good name and ensure the customer has a good experience. Once you understand what is going on and its potential for further problems the answer is no, you can just replace the batteries that are bubbling or show a low voltage after being disconnected from the bank overnight or longer. Once you remove the batteries with shorting cells form the bank things should go back to normal BUT remember you will have two new and two old batteries so in view of the failures so far we can be fairly sure the remaining two old batteries will fail sooner than the new ones. When one does short it will start to discharge the new batteries leading to sulphation and loss of cyclic life so it should be removed form the bank PDQ. If you are happy to inspect/test the batteries on a very regular basis so you identify and remove a failing battery just replace the faulty ones. If you want an easier life with less to worry about replace all four now.

Robmarkham
Robmarkham

Posted: Mon May 08, 2017 7:12pm

Post Subject: Leisure Batteries

Tony, thank you so much for your help. I followed all of the info you gave and feel I now have more knowledge of what I should be looking for. I think I will change the "duff" one and check the others more often and more closely. Thanks again.

Most Read

Newsletter Sign Up

Canal Boat regular newsletter
Sign up to receive our regular email newsletter

Our Privacy Policy

Like us on Facebook



Follow us on Twitter

Cache: Disabled for this object  Total Queries: 43.  Total Objects: 162.  Total Unserialized: 3. Total Runtime: 0.91 seconds.