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Posted: Tue Apr 16, 2019 8:30am

Post Subject: Battery Advice

I have a question related to battery types and whether it is ok or best not to mix different battery types in different banks. We bought our holiday narrowboat in Oct 2010 when it was 6 years old. It had 6 batteries in three banks. A wet flooded starter battery recently replaced by the previous owner, an AGM 160 dedicated to the Eberspacher heater, and the domestic bank with three AGM 160s and 1 wet flooded lead acid recently added by the previous owner. It turned out these three AGM160s were all dead so I replaced them with three wet flooded lead acids to match the odd one. I also added an 80W solar panel which does an excellent job of keeping the batteries topped up when the boat is tied up in the marina. Unfortunately the solar charger/regulator only has two channels so it is generally set to charge the domestic and heating batteries. I also added a 20A battery charger, for occasional use when we are on board and mains hook up is available. This has three channels capable of charging all three banks. With both the solar regulator and charger it is possible to set the battery type - but it has to be the same for all the banks - so I set it to AGM. I hate checking/topping up the levels on the batteries as they are on the swim and very awkward to get to. Hence I vowed as they die I would replace them with maintenance free types. The starter battery failed last summer (after 8 years) so I replaced that with a flooded maintenance free type. One of the domestics failed in 2015, but the other three soldiered on and now into their 9th season are still ok, but I don't think will last much longer. However the odd AGM160 heating battery has now failed. It is marked April 06, so has done very well. My question is should I replace this battery with a similar AGM (probably a 130 due to price of the 160s), or go with a cheaper flooded maintenance free type. I wonder whether I would be better having the same type of battery in all the banks, so the charger, etc, can be set up correctly for all three. I also think I read (but may be incorrectly) that for occasional use it may not be worth spending extra money on better batteries that offer more cycles if the sulfation destroys them before they fail due to cycles. Any advice welcome. Thanks for your help.


Posted: Tue Apr 16, 2019 12:39pm

Post Subject: Battery Advice

There is no easy answer to this and to start with we need to know the recommended and maximum charging voltages for the AGM batteries. Not all AGMs are the same and one well advertised supplier seems to demand a charging voltage that in most cases can only be achieved by a £300 charging system add on. In the past there have been AGM batteries that demanded a much lower charging voltage than that normally set by the alternator. So unless you have all the date for your batteries it is not possible to recommend. Modern flooded lead acid batteries tend to use lead calcium plates where as older and more specialised batteries used lead antinomy. Lead antinomy are likely to start gassing at around 14.2 volts where as lead calcium of any type are unlikely to gas until 14.7 or 14.8 volts. So as long as any maintenance free or open cell batteries are lead calcium there is every chance (having checked the AGM's data) that they can be charged at the AGM setting. Even if as open cell battery did gas a little it would probably be good for it in boat use as long as you kept it topped up. Your battery set up is not of the optimum. The deeper a banks discharge the shorter its life so the normal recommendation would be to make your heating and domestic battery one larger bank so the total discharge is a lower percentage of bank capacity. However you would have to ensure the maximum/recommended charging voltages for all types are within one or two tenths of a volt. I would also point out that placing a Voltage Sensitive Relay between any two banks (subject to voltage checks) would ensure the two banks are isolated when no charging is taking place but are both charged soon after charging starts so you really do not need a three output solar controller, especial for only 80 Watts. If you linked the heating and engine battery by VSR the solar would charge all the batteries after an initial period of charging the bank with the greater degree of discharge. Apart from early in the charging cycle when the charging devices' maximum output is the limiting factor for the majority of charging it is the BATTERIES that determine the charge rate at any given voltage so providing whatever voltage charging is set to does not exceed an individual battery's maximum then you can if you wish mix types, especially if they are in different banks. I am sure that once you manage to get the maximum charging voltage data (this can be very difficult) it will be obvious if you can mix types.

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