Voltage at the battery at idle?

What should the voltage be at the battery with the engine idling?
Yamaha 200HP oX66

They will vary from 12.0 to 12.8 as not all charging systems and battery`s are the same. Idling after a good run slightly higher. After first start less.

Gary is correct.

At idle there will be little or no charge available for the battery. So its voltage will be almost fully reflective of its actual state of charge level which we can't tell you because you didn't tell us whether it's morning and was just charged or is at the end of a long day after running live-wells, graphs or boat lights for hours.

What is the best way to tell if your charging system is working? Was fishing all day and my motor would just turn over but not enough to start. Showed around 11.5V at this time. Replaced battery and fished next day with no problems. After I got home and a few days later I checked the original battery and it showed 12.5V.

While fishing I have live wells, graphs running (4)

Having to put a 1000CCA starting battery`s on boats with these new electronics.

The engine should charge at idle or extended idle times will kill your boat. Charge voltage for a 12v lead acid battery is around 13.8v. Measure battery voltage, engine off. Crank it up and measure again. Idle up to high idle, measure again. Each measurement should be slighter greater than the one before it.

How much alternator is on boats these days? Should be pretty good sized.

Cast is a 100% right.

Battery can show a full charge but can have a bad cell. If it is fully charged, take it in and let them put a load test on it. Sounds like it will fail.
My last battery was less than a year old. had to jump it at the lake to get it started. Showed it was getting a charge as I drove it around letting it charge. Showed to have full charge like yours but not enough umph to crank the motor fast enough to start it.


Your fish finder will probably have a voltage reading on it. You should see the voltage with engine off, higher voltage at idle and higher at driving speeds. It might not be the most accurate but it will definitely let you know if it isn't getting a charge going to the battery. I'd also set it for an alarm at whatever the minimum voltage you need to crank your motor to warn you when You've been sitting and draining it too long on the lake.

Your battery should never show below 12.2v. 12.2 is your 50% depleted point. With lead batteries going lower will hender it's performance and ability to charge.

Battery`s on bass boats go below 12.0 volts all of the time while bass fishing with fish finders, GPS units and aerators running. That is why it is necessary to have a 1000 cca battery for your cranking battery.

I have replaced one vehicle battery and 2 boat batteries in the last 3-4 years and all of them read at least 12 volts but did not have the amps to crank the motor. All had dead cells and would not take or hold a charge. One was under warranty and I argued with the store manager because she wanted to keep the battery over night for testing. It got pretty heated and she finally gave in.

This is pretty much two different conversations. The voltage indicates battery charge level (and charging system effectiveness). If the battery voltage falls below 12 v, I would be very concerned.

The CCA (cold cranking amps) rating is about the plates inside the battery. How many electrons can they store? If the battery is not at full charge, you do not have a full electron load and, trust me, you don't have full rated CCA.

If I got another bass boat, which I will not do, I would have at least three big batteries. One would be dedicated to cranking the motor and nothing more. The motor would maintain its own battery. A matched pair of massive deep cycles would power the twelve volt trolling motor, and charge with shore power. If I had a boatload of electronics, I would install a fourth big battery dedicated to the electronics. The motor would charge this battery too, but I would install a spare battery charging system to isolate the dedicated motor cranking battery from the electronics drain.

Technology is your friend. Buy good stuff. Buy once, cry once.

And BTW, most batteries fail when the lead flakes falling from the plates (entirely normal) pile up on the battery bottom deep enough to short out a cell. Look for batteries with a deep waste reservoir. They last much longer.

Batteries with a badly shorted cell won't reach the proper voltage level (which can vary slightly depending on battery specs). That's actually above 13 volts for virtually all flooded cell batteries. Many spec 12.5V no-load as an approximate 50% discharge level. A battery with a shorted cell will fall on it's face immediately when subjected to a load test. That's often the best way to argue a point of a bad battery. Another is to use a hydrometer to show how 5 cells are charged, and one is a door stop. I don't go for the "if it takes a charge it's good" line of BS. You might get a battery to show a decent voltage with no load immediately after charging, but one hit from a load test will crater it pronto.

Best way to confirm your engine's charging output capability is with an Amp-meter and use of a loading resistor.

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Even on a 50amp capable outboard engine's alternator, typically there will on most boat setups be no charge whatsoever for use by the battery at idle speeds as the loads of the boat's sonar/gps electronics, livewells and accessories easily exceed the small current being output by the alternator.