Posted: Wed Apr 11, 2012 7:32am

I am currently in the process of revising the the electrical demand on our narrowboat changing as many items from 240v to 12v,lights where practicable to LEDs etc and now wish to replace the batteries.The boat is currently fiteed with 4 x UK Giant 110UKG 12V AH(20h) 110amp batteries,one being used as the starter and the other 3 as leisure batteries.Is this a common practice as i would have expexted a different type for the starter,or are some batteries quite capable of dual purpose roles.As the cost of replacements are not cheap I want to buy correctly.Also as our current mooring does not have access to 240v mains hook up is it worth adding a 4th leisure battery space permitting,the engine is a vetus 4 2 1.7 fitted with a 110amp alternator and during the spring also hope to fit a solar panel to help with topping up the system.Yours thoughts and suggestions on bateries would be appreciated,I would think gel batteries would be over budget at this point in time yuors sincerely mark smith

Posted: Wed Apr 11, 2012 8:59am

First of all I note that you do not say how you use the boat. I assume that it is a typical holiday and weekending boat. I have been unable to find the full technical specification on-line for your batteries so can not comment on their suitability for both domestic and engine starting use. However the small amount of detail on the Plymouth Batteries site suggests that perhaps they are not best suited to engine starting. I can not comment on the need for a fourth domestic battery unless I can see the full power audit and charging calculations. You will find examples in both sets of notes on www.tb-training.co.uk. If three batteries have enough capacity (from the calculations - NOT the label) to support the demand for the periods when you are not running the engine then there is no point in fitting another. You do not specify the size of solar panel you are thinking of fitting or the type and source of the controller so I can not factor its use into my suggestions. Batteries have a finite life measured in cycles of discharged to charged. In general the more you pay the greater the cyclic life but to be sure you really need to check the makers technical documents. The lives can typically be between about 150 and 1500 or more cycles. However without a regular means of fully charging the bank (and to do so from the engine alternator would probably take well in excess of 12 hours with the last 8 hours or so at very low current)chemical changes within the partially discharged batteries would cause them to gradually loose capacity. This is known as sulphation and it is what normally renders the batteries on boats without shoreline charging unusable. Typically the battery life will be between 2 and 4 years and this would apply to whatever battery type you bought as long as the capacity was measured at the same (20 hour) rate. This being so the normal recommendation for people in your situation is to buy ordinary open cell wet lead acid batteries. These are easy to obtain, will probably be the cheapest, are easy to top up and more importantly easy to assess for faults with a hydrometer. If the batteries can still supply the load when the engine is not running my advice is not to replace them until a fault develops or they can no longer supply the load. Try to buy from high volume sales outlets so you get fresh batteries than have not been standing for months. Tony Brooks

Posted: Wed Apr 11, 2012 8:05pm

dear tont thankyou for your reply and i appreciate somre detailwas omitted however for a startet battery what capacity/rating would you recommennd and when trying to compare the vast array of supposed best on the market leisure batteries that essentially the greater weight(if comparing similar dimension of battery) would usually correlate to thicker plates and hence a larger no of cycles prior to sulphonation yours sincerely m smith

Posted: Thu Apr 12, 2012 9:22am

Your engine manual should give you the capacity of start battery recommended. Nowadays a start battery should be rated in Cold Cranking Amps (CCA) and there is no reliable conversion between CCA and Ah capacity. Before CCA a typical starts battery for something like a 1500cc marine diesel would be between 75Ah and 100Ah. Something between 600 and 700CCA should do. Higher capacity is OK but costs more. The plate materials, how they are constructed and supported are probably far more important than absolute thickness in relation to cyclic life than just the weight but common experience seems to indicate weight is a fair "easy indicator" for use in deciding which battery to buy. I will not comment on this but would refer you to the individual manufacturers' technical data sheets. I must take issue with the way you seem to conflate the speed of sulphation with cyclic life. I thought I had already explained that cyclic life is inherent within the battery design and manufacture where as sulphation is a function of your inability to maintain 100% charge for the vast majority of time. They have no relationship other than if you persistently heavily discharge a battery (so it is flatter for longer) you will use up cyclic life far faster than if you only lightly discharged it. 6 months life for a battery that is fully discharge every day or so and never fully recharged is probably perfectly acceptable (and you would not get any warranty honoured because it had been abused and not suffered a manufacturing fault). If you paid £1000+ for a bank of 2 volt traction cells, they would be heavy, you may well get the impression that what you appear to think about cyclic life and sulphation is true in that they would take far longer than "normal" batteries before sulphation reduced their capacity to an unusable level. However this would be very misleading because they would have been Ah rated over 5 hours rather than the 20 hours normally used. The way batteries capacities are affected by the rate of discharge means that a 5 hour rated 100Ah battery when tested over 20 hours would turn out to have a very much higher capacity. This means the apparent correlation between weight and resistance to sulphation is no such thing. It is a correlation with the amount of capacity the expensive battery starts with. I have no intention of recommending a particular battery brand/make/model because I doubt there are now any UK battery manufacturing plants for general lead acid batteries and probably well under 10 worldwide. There is a vast amount of marketing differentiation by the application of labels or specifying case colours. You will also find that the length of the warranty is often related to price but take care because the warranty is against manufacturing defect and not customer abuse. The price relates to the number of batteries the vendor thinks will have to be replaced within the warranty period and what that will cost him. If you can find a local battery specialist outlet then take their advice and check what they say with the technical documents that they should have available. Finally I am concerned about your use of the term "leisure batteries". Technically there is no such creature - it is marketing speak. Another highly qualified person has made a public statement that such batteries were all constructed as starting batteries and then went on to invite anyone to sue him. No-one sued. Draw what conclusion you want from that. The point is that you want adequate life from whatever battery you buy and as long as you get it the underlying technology is not that important. Trucks with sleeper cabs etc. have forced the battery manufacturers to really up their game so it is probably now true that a "leisure" or "dual purpose" battery will today give most boaters an adequate life PROVIDING they understand the issues and do not expect the impossible. Such batteries will be relatively cheap and readily available. Only if you have a method of ensuring a FULL - 100% recharge at least every week would it probably be worth paying more to gain more cyclic capacity so until you provide a regular shore line charger or if this is a weekend and holiday boat a 100 Watt + solar array and controller you might just as well buy the wet, open cell dual purpose batteries because you will kill them with sulphation before you run out of cyclic life. Again PROVIDING your power audit and charging calculations work out and you stick to what they tell you. Tony Brooks