Battery Recommendation

[rbrtmccorkle]

sorta on the same topic - I have a 98 Bav Ocean 42 - Currently running 3 Lifeline AGM Batteries rated at 105 Amp each of unknown age - but they are done.  Looking to replace and wonder if there is a consensus as to how many Amp hours I should be looking to replace with - New AGM batteries of the same size come in at 200+ amp hours - so am thinking replacing with 3 of same should produce plenty of power.  The boat has original fridge, small microwave, new raymarine chart plotter and Radar, original raymarine auto pilot and a VHF.  Not much else.

[Symphony]

The capacity of your house bank (I assume you have a separate engine start) depends on two things. First your pattern and extent of usage and second you method and capacity for charging. Generally speaking the higher your daily power usage the higher the capacity of your bank. You then need to be able to charge the bank effectively to replace the power used.

So a cruising liveaboard will have a big bank and multiple means of charging such as higher output alternator, solar panels, wind generator etc, plus probably some form of charge boosting to maximise generation.

On the other hand a weekend plus summer cruise user would be OK with a smaller capacity bank if he is able to rely on shorepower to keep the batteries topped up when the boat is not being used.

A capacity such as yours is common for this type of use - I have the same in my 33. If that is how you use your boat then replacing with similar capacity is sensible as you should be able to keep within the rule of not discharging more than 50%. without additional means of charging the alternator on the engine should be able to recharge most of your usage if you do the typical hours motoring that many people do. Plugging into shorepower will help get the last bit of charge in.

The most useful add on for the battery system is a battery monitor which will give you some hard data about your usage and the state of charge of your batteries. this will in turn inform your decisions about both appropriate capacity and charging.

[Craig]

If your previous batteries have lasted for a long time and your usage has not changed, replacing with similar sized battery bank should be OK, however, to be sure, go through the methodology mentioned by Symphony.

The one thing that worries me is that you mentioned a microwave. If this runs through an inverter then you may wish to beef up your batteries a bit more. A 800W microwave ( microwave output, not power input) actually draws approx. 1.5 times that. That could mean a 100 amp draw on the batteries. Even for 4 or 5 minutes that may kill your batteries unless you only use the microwave when on shore power or when you are motoring.

Craig
"Shirley Valentine"
Gold Coast
Australia

[rbrtmccorkle]

Thanks for all the replies -  The previous batteries are of undetermined age, but probably over 5 years old.  Combined Amp hours of the 3 AGM batteries was 330 amp hours and for the year plus I've owned the boat they have been sketchy.  I'm living aboard the boat now - mostly on shore power as I complete outfitting for a multi year cruise.  Here is what I ended up dong.

1.  Built a Solar Arch over the Stern.
2.  Added 450 Watts of Solar
3.  Added 450 Watts of Wind generation
4.  Replaced the 330 amp hour of batteries with same brand but now rated at 660 amp hours.  Went with same brand because I'm in a bit of hurry to do some sailing and the path of least resistance in terms of replacing was to use all the same cabling and space.

We'll see how it works out - but I can't imagine this not being a improvement.

Bob