Posted: Fri Sep 07, 2012 7:17pm

Dear Sir, Can you advise me on batteries I have had replaced recently? I have a 52ft Narrowboat fitted with a Mastervolt Dakar Combi model Dakar 12 / 1500-65 / 230V / 50Hz. The 4 old 110ah domestic lead acid "wet" cell type have been replaced with 4 deep cycle gel type batteries of the same rating. The existing "wet" type lead acid starter battery remains, as it still has life in it. I had this work done about 5 months ago. Initially the system showed 100% charged when maintained on a land line. We went out for a short cruise and used the inverter to watch TV etc. as usual. The indicated charge has never returned to 100% since, despite the engine running all day when cruising and being connected to a land line in the marina. I checked the manual and I note that mixing the two types of battery should be avoided, but it does not say why. recently I have run the batteries flat. I noted that despite the charge indicator registering 0. All systems continued to run for a whole weekend and the best part of the next! I thought this would re-calibrate the system. Re-connecting to the landline resulted in the batteries charging to an indicated 60% over the week. the system will go from Bulk to float fairly quickly if i turn the system off then on again at this indicated charge level. Is this a calibration issue or a battery type mix issue? will the batteries be fully charged even though the system only shows at best 75%? Thanks in advance for your help. Regards Peter Owen.

Posted: Fri Sep 07, 2012 9:05pm

Dear Peter, I am afraid that the forum is not very good for this type of answer because it will not allow paragraphs so you get one large chunk of text. The easy answer is the reason for not mixing battery types. Gel batteries typically have a maximum charging voltage of around 13.8 volts where as for wet open cell batteries it is around 14.5 volts so if you mix them you either undercharge the wet open cell batteries and this leads to a loss of capacity by sulphation or you overcharge the sealed batteries which will destroy them. My initial fear is that your charger has been left set for wet open cell batteries and now the gels are damaged. The online manual for your combi-unit makes no mention of a battery monitor so I have no idea what is giving you your percentage of charge figures. If it is an amp hour counter (which most apart from the Smartgauge are) then it is almost certainly telling porkies unless you very regularly fully charge the bank and re-synch the counter. If you are using voltages then unless the batteries have been left to stand for many hours without a load it will be somewhat unreliable. Then we have the problem of adaptive charging where cleaver chargers try to work out when to go to float. Unfortunately they often/sometimes go to float too soon leading to not so well charged batteries. As I said I suspect your gels may have been damaged by charging at too high a voltage and their different �resistance� characteristics may be fooling the charger to go to float too soon. The gels may now only have a fraction of their original capacity because they have been forced to gas driving off the liquid in the gel. I honestly do not know and think that you need to take them to a real battery specialist for testing. I feel that 75% may be 75% of the original capacity but it is 100% of the present capacity. Personally I would not mix types and given that boat batteries are best thought of as consumables I would not spend money on anything other than some form of wet open cell batteries. Tony Brooks