New battery

[buhfee]

Gday guys, just after a little input on what kind of battery I should be looking at for my boat. All the battery needs to run is some navigation lights, sounder/gps, occasionally a spotlight and I would also like it to start the motor so Im thinking a marine battery would be the way to go rather then a full deep cycle. I have no idea how many CCA it should be or anthing though. My motor is a 70hp Evinrude VRO. Thanks for any input guys!

[Testlab]

I think you need around 550 CCA which will be around 80Ah reserve capacity. Most batteries will be able to supply this but you will need to watch the load you plan to run and the time you plan on running it for.

An 80Ah battery will supply a 5A load for 16 hours (80/5=16) but you can only rely on say a third to half of that time if you also want to use the battery for starting. The time you can safely run your load and start will depend on the charge level in the battery at the beginning, temperature (cold reduces capacity a lot) and overall age/condition of the battery.

A Lowrance HDS-5 draws 1A but larger or older sounders can draw 3A, and old style light globes draw around 1A each so it adds up pretty quickly. This is why two batteries are usually best for serious applications but a good quality and well maintained single unit will be fine for light duty use.

[buhfee]

Ok thanks mate! I think one will be fine then as I live in Bathurst and only go to local dams and have usually left by dark anyway so the navigation lights and spotlight are rarely turned on. Thanks very much for the quick reply!

[oz_brett]

I wouldn't be to concerned with it being a marine Battery, if your car battery is about the same CCA I would be just buying a maintinence free battery to suit the car that way you can swap them back & forth every couple of weeks to keep them both in good condition, this not only keeps your boat battery maintained also gives you a back up for when you need the car & the battery is dead.

[GaryO]

A car battery is a lot cheaper , with the change by a jumpstart unit as a backup for the boat an also can be used for the car.

[dogbox]

Marine Batteries are constructed differently to deal with the thud of rough water, Yes car batteries work but they are subject to shorter life.

When it comes to charging life, every time a battery discharges the plates inside break down, the harder, faster a battery has to work, discharge, the sooner it will need to be replaced.

Next time your at the auto shop have a look at how many of the batteries have a Taxi clause on them, Taxis Punish there batteries and battery companies who sell lesser quality batteries will have this cause and are generally cheaper.

For me the best battery for any application is the one with no taxi clause, maintenance free and if you need it for a boat then by a battery for marine application.

Dogbox

Edited June 2, 2012 by dogbox

[oz_brett]

when I bought my boat new it was fitted with a marine battery in the first week I added a second battery using a maintinence free from nrma its now been over 4 years and done 400hours mostly offshore.

recently done an overnight chasing jews on the hawksbury & didnt even look like having to change batteries (used the nrma battery all night and starting to go home)

Both batteries are still going strong.

[mike82]

Good quality marine batteries are constructed very differently from automotive batteries. They are designed and built with the different application and different style of usage in mind.

A good quality marine battery is more expensive than a car battery of the same size because:

1: They have sheets of fibreglass separating the plates for vibration resistance.

2: They have a different plate design also for vibration resistance but more so to suit the application and "cycling" of a marine battery where after starting there is not a large alternator to recover the battery (like in a car) so they are designed to charge faster.

3: Most will be a semi deep cycle construction. Whilst not a purpose deep cycle they will be built to handle repetitive light charge/discharge cycles.

An automotive battery is designed to provide a large staring current in a short burst then be recharged by the alternator before doing it all over again.

While a boat battery is designed to provide the start current, get a light charge, then provide power for lights, radios, sounders, bait pumps etc while anchor, then provide a start current and accept a light charge current as fast as possible on the way home.

So while a car battery will work, there is a reason why they design and make a marine battery, and why they are more expensive, and why they will last longer.

[kyngfish]

I have been told that a Truck or 4WD battery is as good as a marine battery.

Is this correct?

[GaryO]

I have been told that a Truck or 4WD battery is as good as a marine battery.

Is this correct?

Well technicaly they arent better , but i guess being bigger than what may be required they will still be effective in doing the job even when they may have deteriorated 10-20% in there performance. End of the day marine is better and is the way to go for bigger boats or boats with a high power demand while anchored but for a weekender a cheaper car battery would be fine and most likely still be a cheaper long term option even IF it does die a bit sooner.