How many volts do you actually measure from a 12v battery?

[Mike 12345]

I had my boat plugged up all last night, charging the trolling batteries. Typically, when I wake up in the morning, the charger will show both batteries with a green light, or charged. This morning I had one green and one still red.

For the last several months I've had the idea that my on-board chargers lights are malfunctioning- sometimes they never show 'green', but the battery will measure nicely between 11 - 12v with a handheld multi-meter. Trolling motor works just fine all day on the water.

I'm no electrician, which is why I ask the question- if your battery is a 12v battery, is a range 11v or better genearlly right in the zone? This morning, the battery showing 'green' measured about 11.5 v and the one showing red was around 11.2.

Thanks

[manveru]

not sure about boats but in cars, 12.6 volts is considered fully charged

[South FLA]

12.6 to 12.8.

If you are getting those readings and your charger is not getting all greens after a full night of charging, then its time to buy new batteries  .

Walmart it with Everstart Marine Maxx or get yourself some nice new Sears Platinum Marines  !

[Way2slow]

The volts are going to depend on the battery manufactor and the electrolite used.  It's not uncommon to see 12.6 volt batteries but most modern deep cycle batteries charge to approx 2.14 volts per cell, 12.84 volts for a 12v battery (that's after letting it rest 24 hours from charging).

The battery is considered 100% discharged at 1.96 volts per cell or 11.76 volts for a 12 volt battery and should never be discharge below 12 volts.

[Carrington]

my two trolling batteries measure about 13v each when fully charged and the cranking is around 12.5v when charged

[s13john]

just curious is that voltage under load or just sitting still ... my trolling motor at the end of the day will show on my fish finder that its pulling around 11-11.5 volts under load and then rebound up to around 12.2+. i have had it dip into the high 10's but its and old battery and plan on replacing it anyway's.

[Way2slow]

That is no load voltage but if you're getting that much of a drop under load, your battery/ies are probably on their last leg.  Too small of a battery cable or a bad connection can also cause you to have more voltage drop under load that you should have.   The best way to check that is, with a good digital meter, connect across the two lead post on the battery the TM cables are connected and see what kind of a load voltage you're getting.  Then connect across the TM connector on the TM and see what the voltage is.  They should be close to the same.   On multi battery systems, make sure the interconnect cables are large enough and good, clean connections on them.

[BLUESKY]

Have you checked the liquid level in the batteries?

[Matt Fly]

a battery can have a dead cell and still read over 12 volts across its terminals.

   The only true way to test if the battery is good is to put the battery under a load,

   and that is best accomplished at Auto Zone for free, or Walmart if its an EverStart series.

You should be able to read whats coming out of each leg of the charger to verify your getting good charging voltage.

    My alternator will read 13.7-14 volts and thats normal in my car, but when she's not running, only 12.8, and thats normal.

    Not much difference in voltages, the difference in all chargers is the rate of charge, the amount of amps the charger is putting out.

    The faster you charge batteries, the shorter the life span, specially on cheaper batteries.

   Always trickle charge at 2amps if time permits, it may take a day, but in the long run, your batteries will last a long time.

   

[Way2slow]

2 amps is fine if you're charging a small lawn&garden or motor cycle battery, but it's not good for any flooded cell, battery the size you would use for cranking or TM in a boat.  If you charge at two amps every time, the battery will stratify on you.

10% of the rated capacity is what's recommend most any flooded cell battery.  So, if you have a 20 amphour battery, charge it at two amps, if you have a 100 amp hour battery, charge it at 10 amps.

[Matt Fly]

as long as you maintain your cell levels, charging at slow rates, called "trickle charge" is best done at slowest rate to save the life of your battery.

  You may charge a car battery that way, but a car battery isn't a deep cycle battery.

[Matt Fly]

To stratify a battery, one would have not charged them on time, another words, to stratify a battery would mean they have been left under 80% of capacity for long periods of time.

   Charging of any kind immediately or soon after use will prevent that, plus, you have to assume that every battery out there is always used to below 80%.

   Like I said, if you charge at a high rate, you fry electrolyte, the slower you can maintain a battery, the longer life you'll get.

[Way2slow]

To stratify, you only have to keep charging at too low of a rate to cause the battery to gas. It take sufficient bubles generated during the charge cycle to rising between the plates to keep the electrolite mixed.

To start to sulfate, a battery has to be left below 80% for as little as 24 hours.

[edit]Unnecessary and rude comments removed[/edit]

[Bassin_0502]

I was enjoying this thread and hoping to really learn something new. Seems to be getting a little rough lately, but hey, what the heck do I know, maybe you guys are best buds and have been discussing this question for some time. In any case, I think it's still an important question (just check how many charging threads come up...). Perhaps a couple (or even 1) references or citations to support your positions would really go a long way. All I know is that I don't have the answer yet.

[Way2slow]

Here's a couple,

9.9. Is Gassing Good For a Wet Battery?

When a wet (flooded) Low Maintenance (Sb/Ca) battery reaches the absorption stage which is approximately 14.4 VDC at 80° F (26.7° C) or 80% State-of-Charge during a charge, it will start to gas (bubble) and is a normal part of the charging process. Gassing is the electrolysis of water into two parts Hydrogen gas and one part Oxygen gas and can be explosive. The gas bubbles given off by the plates will help to mix the electrolyte as they rise to the surface. This will help to prevent electrolyte stratification. Electrolyte stratification is acid concentration that is greater at the bottom of a battery than at the top, especially within batteries with more than 100 amp hours capacity. Normal charging should produce moderate amount of even gassing of all cells, which is good. Overcharging a battery or rapidly charging with high voltage will produce heavy gassing, heat, consume excessive quantities of water, accelerate positive grid corrosion, warp the plates, and is NOT recommended. Ventilation is required for all lead-acid batteries and good ventilation is mandatory for wet batteries to dissipate the explosive and toxic gasses produced during charging.

9.7.3. Size the charger based on the discharge amount and how fast you need to use the batteries again. Slow recharging is recommended, so chargers that are sized 10% of the capacity of wet, AGM (Ca/Ca) or Gel Cell (Ca/Ca) VRLA batteries should be used

The best way to prevent sulfation is to keep a lead-acid battery fully charged because lead sulfate is not formed. This can be accomplished in three ways. Based on the battery type you are using, the best solution is to use an external charger in a well ventilated area that is capable of delivering a continuous, temperature compensated "float" charge at the battery manufacturer's recommended float or maintenance voltage for a fully charged battery. For 12-volt batteries, depending on the battery type, usually have fixed float voltages between 13.1 VDC and 13.9 VDC, measured at 80° F (26.7° C) with an accurate (.5% or better) digital voltmeter. [For a six-volt battery, measured voltages are one half of those for a 12-volt battery.] This can best be accomplished by continuously charging using a three-stage for AGM (Ca/Ca) or Gel Cell (Ca/Ca) VRLA batteries or four stage for wet (flooded) batteries, "smart" microprocessor controlled charger. If you already have a two-stage charger, then use a voltage-regulated "float" charger or battery "maintainer", set at the correct temperature compensated float voltage to "float" or maintain a fully charged battery. If you need Web addresses or telephone numbers of charger manufacturers, please see the Chargers and Float Chargers and Battery Maintainers sections of Battery Information Links List. A cheap, unregulated "trickle" or a manual two-stage charger can overcharge a battery and destroy it by drying out the electrolyte.

A second method is to periodically recharge the battery when the State-of-Charge drops to 80% or below. Maintaining a high State-of-Charge tends to prevent irreversible permanent sulfation. The frequency of recharging depends on the parasitic load, temperature, battery's condition, and battery type. Lower temperatures slow down electrochemical reactions and higher temperatures will significantly increase them. A battery stored at 95° F (35° C) will self-discharge twice as fast than one stored at 77° F (25° C). Standard (Sb/Sb) batteries have a very high self-discharge rate; whereas, AGM (Ca/Ca) and Gel Cell (Ca/Ca) VRLA batteries have very low rates.

Now, ya'll have a nice day.

[urp]

The best battery ck is under load. Put a 150 amp load on it and it should maintain 10.6 v.