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Old 12-12-2012, 13:06   #1
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One Battery for Motor and Gen

My battery for the engine died. I am in a place where you can't just go to the local store and buy a boat battery. You can buy car batteries. I have a battery for my generator that is good. So is it ok to connect both the generator and the engine to one battery? At times the engine and the generator, both with alternators, will be running at the same time. I read in one thread that it is not good to have 2 charging sources on one battery. Also I am under the impression that it is a bad idea to use car batteries because they aren't made for the bouncing and generally won't last very long. But other than that if the battery has sufficient cranking power it should not matter if it is a car or maine battery, right?

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Old 12-12-2012, 13:51   #2
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Re: one battery for motor and gen

There are disadvantages. Consider a situation where THAT BATTERY is dead. Now you cannot start the engine and you cannot start the genny to charge the engine's battery so it can start. Mine are separated.

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Old 12-12-2012, 14:08   #3
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Re: one battery for motor and gen

If you can buy a car battery, go ahead and do that. It may not last as long as a marine battery, but many so called marine batteries are the same as car batteries.

It won't hurt to hook up two charging sources to one battery. But I would prefer to have separate batteries for redundancy as you said.

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Old 12-12-2012, 14:09   #4
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Re: one battery for motor and gen

One battery, two engines, no problem with two alternators charging one battery. I share a battery between my generator and port engine. My house bank that starts my starboard engine and I have a crossover switch in case of a dead bank.
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Old 12-12-2012, 14:15   #5
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Re: one battery for motor and gen

it would help to know more,(size of loads,etc) but car batteries will do just fine for a year or two

we have lived on 27 series batteries for up to three years ,1 ,as starting and three as a house bank . but get one for a spare Ole
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Old 13-12-2012, 10:10   #6

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Re: One Battery for Motor and Gen

Car batteries conventionally are SLI (starting, lights, ignition) batteries designed to be discharged less than 10% and then recharged immediately. Boat batteries are usually deep cycle batteries, designed to be discharged 30-50% before recharging.

The key difference for you is probably that an SLI battery can be destroyed by deep cycling it (80% or more) are little as a half dozen times.

Both will start your engine, but the SLI battery will not last long if you are using it as any kind of deep cycle house battery.

You often can find a deep cycle "car" or "RV" battery in the same place that just sells car batteries. That may actually be the same as some marine deep cycle batteries.

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battery, motor

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