Hi Mr. Mac
Boats with large engines which cannot be easily hand started need to have a dedicated battery for engine starting. I assume you are able to start your 9 hp with the pull cord if necessary, thus I think a second battery is needless weight, expense and complication.
Kind regards
Hugh
I tend to agree here....
when you hit the start switch on a small outboard, the battery isnt being hit with a 150-200 amp draw all of a sudden.... a 10hp outboard will draw about 50-60amps during startup so it wont be hurting the battery like a big load would....
and with the back up pull starter, you wont be without a way to get the motor started even if you run the battery dead.
no matter how many batteries you install, if you dont have enough charge capacity to keep the single battery you have charged up with the electrical demands that you have, all the other batteries are just dead weight and wasted money in the boat.
to explain.. one of the worst things you can do to a battery is draw it down below about 50% of its capacity... and you cant tell this by how dim your lights are getting, because by the time the lights start dimming, you are way, way lower than the 50% limit...
so at this point you are damaging the batteries.
you can have more batteries to carry and deliver more total amps, and if you dont draw them down too far you will be fine, but how do you know where you are at on the state of charge? because when they are below the 50% limit, all you have are more batteries being damaged....
batteries do have a life expectancy and drawing them down too far is greatly shortening that time. from 5-8 years to 2 years or less...
assuming you paid money for them and they will need to be replaced again after they go bad (usually about 2 seasons), this is bringing the cost of operating the boat up quite a bit. and the extra battery(s) is/are taking up space, weight and maintenance time in the boat, as well as wasting money because it could all be prevented by the addition of the proper size solar panel to begin with.
some boats need more than one or two batteries because of their exceptionally high power demands or a dedicated starting bank, but for our smaller boats, 2 batteries are plenty and for most of us, 1 is sufficient.
it depends on how long you plan to have a boat, but a good investment on a boat is a good solar system, and if you get a quality setup, you can always remove it from the old boat and use it on the new one when you upgrade. its an investment that pays for itself....
in general there are only 2 types of solar installs that are done on boats.... the type that gets installed on boats that dont get used much, barely adequate to keep the single battery charged when no one is around.
and the type that gets installed on boats that people use often and is depended on to deliver when the switch is thrown, it makes no difference how many batteries the boat has cuz the solar array is sized to match the bank, usage and weather conditions for the area....
the second type of install is the one that can be referred to as an investment because it can add more actual value to the boat than the actual cost of the components, where the first type of install does not add value because it is an insignificant addition, even though it may keep the battery charged as long as it doesnt get used much...
understanding the batteries, how they work and how much demand is going to be placed on them, will determine how many you need in the bank, and these two factors will determine how much charge capacity you will need.... and understanding how solar controllers work and how panels are rated will help you determine how big of panels you should have to build a system you can depend on for many years to come.
