battery-voltage-condition?

[Rickk]

I see that some of you use a volt meter to check the charge of your battery,..is this an accurately way of doing this?,..(I alwayed used a Specific gravity tube,.. hassle/messy,)..if a volt meter works,..what voltage to you expect?

[MK]

A volt meter is good way to tell if a battery is discharged or mostly discharged. However, a fully charged battery will read about the same volts as a partially discharged battery, about 12.6 volts without any load on it. A battery fresh off of the charger might read a shade higher.

If the battery is in a boat or car (not running) and under a load such as some electronics, radio, etc and still reads 12.6 +/-, you are probably in good shape. If it drops to much below 12.4 or 12.5 v. under a light load, it needs charged. The specific gravity check you mentioned is the best indicator of charge level but this can be a pain, not to mention leaving drops of acid where you dont't want them.

If the boat is running, the voltage should be 13-14v if the charging system is working properly.

[Boatnut]

MK,
what if the batteries are sealed gel batteries? any easy way to "load" test them?
thanks

[Hawgeye]

There was an article in Bass and Walleye Boats about 6 months ago I think on what different ways to test different types of batteries with different methods. Using a voltmeter works very well as long as it is a very acurate meter like a Fluke. If I can find the article I will let you know. Gravity test is usually pretty accurate. As one mentioned earlier, as a battery sits for awhile somewhat depleted, if not under load will tend to indicate a higher charge. If you put a load on it like a radio for 5 minutes or so, you will see the battery voltage drop more quickly than when fully charged.

[MK]

Boatnut

I've never tried it on a gel-cell. I know the voltage on the lead-acid will remain close to 12.6 v. until it get pretty well discharged and then the voltage drops off sharply. I can't say for certain if the gel-cell has the same characteristics. It may have a more gradual voltage drop-off and if so, a voltmeter should work better on them than on the wet models. The output voltage may more closely track the actual available charge (power) left in the gel models. For example, a lead-acid with a no-load voltage of 12.0 volts is nearly dead but the gel-cell may still have a lot of power left at a reading of 12.0 v. no-load. I'll bet another reader will have more info on this. Sorry I can't be more help.

[JCarp]

www.marine-electronics.net/techarticle/battery_faq/b_faq.htm


Worth looking at.

[Airwave(OH)]

Mike this sounds like a smart A## answer but You can buy a load tester. I believe at Napa stores. It is the best way to check em. Thats how we check em at the shop. It will tell you if any cells are bad. I don't believe they are too expensive. If i were at the shop I could tell you. I will find out for future reference.

[Box]

There is actually an article in the new Bass and Walleye Boats mag about just this issue. I'd rather you read it than have my fat fingers mess up the numbers :)

-Box

[perchjerker]

Mike-
The easiest way to load test a battery without a load tester is to put a voltmeter on the battery, preferably a digital one, disable the ignition, and have someone crack the engine over while you watch the meter. Make sure your battery terminals are clean (take them off and clean the posts, too). You will get an accurate reading unless you have a starter that is drawing too much current and sucking down your battery. In most cases, it works, though.

[The Smalleye]

The best way to get the state of a battery is to load test it, you can take them to most battery stores and they will do this for you. If you do this yourself BE CAREFULL THEY COULD EXPLODE so use the right protective equipment like gloves,safty glasses. Hope this helps you.

[Rickk]

Sure does,...great help from you all!,...is this the greatest site or what?..................................

[Someday]

This is from Trohan Battery's Website:
TABLE I. State of charge as related to specific gravity and
open circuit voltage

Percentage of Charge Specific Gravity Corrected to
80o F Open-Circuit Voltage
6V 12V 24V 36V 48V
100 1.277 6.37 12.73 25.46 38.20 50.93
90 1.258 6.31 12.62 25.24 37.85 50.47
80 1.238 6.25 12.50 25.00 37.49 49.99
70 1.217 6.19 12.37 24.74 37.12 49.49
60 1.195 6.12 12.24 24.48 36.72 48.96
50 1.172 6.05 12.10 24.20 36.31 48.41
40 1.148 5.98 11.96 23.92 35.87 47.83
30 1.124 5.91 11.81 23.63 35.44 47.26
20 1.098 5.83 11.66 23.32 34.97 46.63
10 1.073 5.75 11.51 23.02 34.52 46.03

8. Correct the readings to 80o F:
• Add .004 to readings for every 10o above 80o F
• Subtract .004 for every 10o below 80o F.
9. Compare the readings.
10. Check the state of charge using Table 1.
I hope this Show up correctly

[Boatnut]

thanks but what if they are trolling motor batteries? do i put a digital meter on them then turn on the trolling motor on hi speed? is that enough of a load?
thanks!

[ebijack]

my own personal experience...if after you let the battery "burn off" after charging (letting it sit at least an hour) the digital voltage should be 12.6 to 12.67. any battery in good condition will maintain 12.6 for a very long time. all the batteries i've had go bad started by only maintaining a 12.54 voltage and by the time 12.4 was maintained the battery was bad enough to where when you checked it with a load tester it wouldn't maintain and hold power..dropped to and below 9 volts. i've used my load tester for years, but now trust my meter. one guy i work with tests batteries every day (electrical lab). they actually test a batteries condtion by monitoring and adjusting the charge/discharge rate(in brief). and monitor the inside temp continuously.
using the digital meter (flute)check hasn't failed me yet.
hopt that helps

[MK]

Not knowing what you have for a motor, battery setup, etc. makes it difficult to guess about your particular boat. If I were you I'd do the following:

1. Fully charge the batteries and check the voltage no load and with the trolling motors on high.
2. Next time you are out, check the voltage after a couple of hours of running the motor. Make the check with both no load and again with full load. Make sure the load is the same, that is, if your first check is with the prop out of the water, make sure the succeeding checks are also with the prop out.
3. Repeat #2 a couple of times during the day and write the voltages down and keep this in your boat.

This will give you an initial reference voltage for fully charged and also for partial charges. It may not be the most scientific method, but it should give you a good idea of what to expect on your personal rig. Make sure you use a digital volt meter.

Some depth finders have a setting where the battery voltage can be shown on the display. I power my depth finder from my trolling batteries and can monitor the voltage from it. Some people disagree with this setup but its never given me problems.

[Hawgeye]

Thanks for that link. I just wanted to post this myth about setting batteries on concrete floors. In a past discussion, I suggested that with todays materials, it is no longer taboo to store your batteries on the concrete floor. That link above has a excerpt on exactly that. Thanks for helping me find some proof for a previous argument.

MYTH 10.1. Storing a battery on a concrete floor will discharge them.

A hundred years ago when battery cases were made of porous materials, such as wood, storing batteries on concrete floors would accelerate their discharge. Modern battery cases, made of polypropylene or hard rubber, which are better sealed, so external leakage, causing discharge, is no longer a problem. However, the top of the battery must be clean and dry. Temperature stratification within large batteries could accelerate the internal leakage or self-discharge if the battery is sitting on a cold floor in a warm room or is installed in a submarine.