Battery Types?

Battery disconnect switches are a great invention. Typically, we will shut off both start batteries and the house battery when we are not on the boat unless we will be off for only a few hours. I've yet to actually need shore battery charging. However, during the off season, I remove all three and keep them in the garage and put them on a full automatic charger once every month. Other than that, they don't see shore charging. Every thing seems to work fine with that protocol.
 
Powerboats have engines with alternators and batteries to charge. So do automobiles. Why do boat batteries require shore power, or other, extra charging to be topped off to a full charge and not automobile batteries?

Just wondering...

Aye.
 
Hey there, Foggy, no bites on this one?

Let me give you my 2 cents worth:

I think it's because auto batteries, maybe the original 'starting battery', has mainly just one job: provide high amps over a short time to start the engine. Once the engine is running, the engine alternator provides all the autos power needs: light, horn, gauges, GPS, cell phone chargers, etc. These batteries usually are not run down past 20% or so. This, plus their physical make up of multiple relatively thin lead plates in acid lend them to being adequately recharged by the engine alternator.

Marine batteries, as I see it, are different. Boat electrical needs are often high when the engine is off, unlike an auto - unless one plays the radio too loud too long and then finds the thing won't start. Been there. Enter the 'deep cycle' battery which is designed to meet long hours of draw down. Most don't take much past 50% draw down without shortening their lifespan. AGMs may stand 80% draw down without suffering much as long as they are recharged. Deep cycle batteries have much heavy lead plates than auto starting batteries - notice they weigh more? This physical difference in the plating relates to the need for longer charging at lower voltage than auto batteries. Of course, there are 'combo' starting and deep cycle batteries which split the characteristics, and charging needs, for the auto and marine types.

That's my story and I'm sticking to it.

Aye.
 
Certainly agree with Foggy's reasoning. An interesting thing is that my 2012 Yukon only runs the alternator if the battery voltage drops or the power draw is increased. The idea is that you will get better mileage with less alternator draw. (I have not gong into the electronics of this), but it bothered me enough to put a SCAN gauge on, so I could monitor the battery voltage. It runs form 12.5 up to 14.1. So this affirms Foggy's thoughts, that even with an alternator which does not run all of the time, you are on the top 20% of the battery.

In a boat which runs a lot of the time, the battery will be charged--maybe even over charged if there is a poor voltage regulator. The inboard-inboard/outboard will have a "smart" regulator. When you are on passage with a trawler--the batteries are always charged, as the car. In a passage making sailboat--just the opposite, where the battery banks are drawn down to 50% by autopilots, nav gear, radios etc--and then a generator is used to bring those batteries up to charged state, heat water, make water, bring down eutectic solution in freezer/refer plates and may even do the wash. by running several hours a day. (I know some boats still use wind vanes...and no power to steer--been there)
 
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