Do not think batteries are made in NZ anymore,so they are imported and sit on a ship in a container for 3+months.Go to store etc and retailer certainly doesnt test charge or trickle them. So if a batterary can travel/sit on a shelf/container.

letsgetem wrote: Its a 90hp Mercury 4 stroke. The battery is 530cca 52AH.

OH! For my 90hp mercury 4S, battery needs to be at least 1000 Marine cranking amps (MCA), 800 cold cranking amps (CCA) or 65 amp hour (Ah). 

dont place too much weight on the published alternator output - it does give an indication but i wouldnt base calcs on these values.

Steps. You may know the answer .I have no idea But why do we have so much trouble with marine batteries.suppose to have plates closer together to impacts etc.yet 4x4 vehicles.cars etc travel on roads with pits holes etc equilvent to driving at sea but not so many issues. Is the marine battery a con?? Older car sitting for 2 months battery 3yrs old and started no issues

The new glass matt batteries are a lot more robust than the older lead acid which haven’t been made for some time. Batteries should always be locked down be it in a car or boat.

The biggest killer of the new glass matt battery is not keeping them charged up, unlike cars, boats sit around and the battery loses charge, amg batteries need a good charger to look after them.

It’s important to have the correct battery for the boat and the electrics on board. Depending on the age of the boat and the type of ignition system some motors require larger batteries so it pays to check the manufacturers recommendation. 2S Hybrid motors like optis and etecs need bigger batteries even for the smaller 90hp motors to keep the battery voltage levels up. If the voltage drops to low the computer will shut down, the motor will sound like it’s winding over ok but it won’t start. Later model 4S use a dynamic voltage ignition system which sense the voltage differently. Too larger battery can be a negative as well. You should always check your battery terminals for tightness and corrosion and I only use Vaseline to coat the battery terminals, spray on oils are conducive and if they are sprayed over the top of the battery can cause the battery to discharge.

Voltmeters are really the only way nowadays to check the change level of the battery, we used to use hydrometers on the old lead acid unsealed batteries which is the best way to check batteries, many times I could pick up a dead cell because the specific gravity would be lower in that cell to the others. Remember digital voltmeters are very sensitive, when you put a sudden load across the battery like lifting the engine or using a capstan, the voltage will drop, normally this doesn’t mean the battery has gone flat it will recover. It’s the continuous loads like fish finders, vhs and stereos that will flatten the battery during the day. This is where keeping an eye on the voltmeter during the day is a good idea, that’s why I like the Ctek comfort light system, easy to keep an eye on and when the yellow light comes on start turning things off. But each to his own.

Hot rated.. in the actual testing section noting changes as battery charge increases.

letsgetem wrote: Ok, Im probably stupid. There Ive confessed. I thought my boat battery was losing charge between trips with the motor charging. But - I was reading battery voltage on my sonar screen. I have now taken battery voltage with a multi-meter directly on the battery (terminals). It shows- Battery voltage, With everything incl sonar off 12.82v With sonar on 12.61v With sonar on, voltage into sonar 12.5-12.6v And, the battery voltage is NOT going down - over 5 days it stayed at 12.82v. This is the voltage after a trip charging the motor. I dont know why the voltage on the sonar screen varies (when battery voltage is constant), but it doesnt matter. It was an interesting discussion, and thank you for your input.

Interesting but as you say you could chase around looking for the answer, you might be better installing one of these

https://www.burnsco.co.nz/usb-socket-voltmeter-flush-mount

I am not surprised by those readings. Wherever you have current flow, connections, switches etc, you will get voltage drop.

Yep , want correct voltages, direct off the battery..The type dash gauge KA mentions are far better than the reading off the gps.. Do not just connect to nearest ground or live wire...ideally run direct to battery, or at least the main buzz bars, clean and check all connections on and between battery ands bars regularly..