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    I have to replace the two service batteries on my N321.
    It is a 2002 model and the set of Exide ones from the factory lasted 7 years.
    They were a truck battery, sometimes called a type 629, 180 AH, 513mm long, 223mm wide and 223mm high. I imagine various other Nauticat types also use these batteries. They are basically a big engine start battery.
    In 2009 I put in Varta Silver M18 batteries of the same size and spec as the original but maintenance free. They have lasted 6 years.

    I now find that Varta do what looks like an identical battery to the M18 which they claim is a dual purpose, starting and deep cycle battery. It is the LFD180 and I can get them from just under £170 each.
    What is surprising is that Varta do not seem to publish any technical data on how many deep discharge cycles the batteries can do.
    All the other batteries I can find of the same dimensions and specs are generic ‘own brand’ types mainly from online retailers, which I’m a bit doubtful about.

    I believe what really canes the batteries is the prolonged use of the autopilot when sailing, which is something we do a lot of.

    I wondered what others owners may have bought over the years? Also any comments on battery usage when sailing.

    Many thanks


    Steve: We have Mastervolt AGM batteries which were fitted by the factory when the boat (a 331) was built. They are now 8 years old and appear to be a s good as new. According to the Mastervolt on board battery monitor they still charge to 100% capacity. They hold their charge through the winter without dropping below 13 volts without being charged as i don’t like leaving the boat connected to shore power for long periods  We use the boat quite a lot and have been down to South Brittany most summers for a twelve week cruise. I have always ensured that the batteries are never discharged below 55% of capacity which i think helps with longevity. We too make extensive use of the autopilot when sailing and the fridge is on constantly. We find we can anchor for three days before needing to recharge i.e. we are down to 55% capacity. Domestic battery capacity is 550 amp hours.


    Thank you for your useful comments.
    I imagine on your boat the ‘extras’ boxes got ticked a few times when it came to batteries and charging, because I see that the standard spec is for 2 x 180ah lead acid domestic batteries, as for the 321.

    I did not realise that Mastervolt made batteries and looking online it is clear they get very good reviews, in line with what you have experienced.

    Doing more research it seems that ‘you get what you pay for’. AGM and Gel batteries cost a lot more but give a longer life, and tend to be designed for deep cycling.

    My limitation is that the battery box will only hold the 2 sized batteries I gave in my first post. Mastervolt only make a Gel battery of that size and they retail for £450 each.

    I guess I will try the Varta LFD180 batteries for now and take more care of watching my battery voltage. I only have the standard voltmeter/ammeter on the switch panel.

    What voltage equates to your 55% discharge rate?




    55 % charge left = 12.3 volts (50%=12.2 volts)

    KInd regards

    Richar White

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