# testing batteries charge



## Al. Countryboy (Oct 2, 2004)

I posted a few weeks ago about charging my marine batteries with my Honda generator that has a built in battery charger when needed. I have been running a few DC lights to try to get and idea of about how long a battery will hold up before recharging. I could tell that the florescent lights were not as bright so decided to hook the battery up to the generator. I left it on the generator for 1 hour and the bulbs seem bight again, but doubt if the battery was fully charged and have read where you want to fully charge them each time. This is an 8 amp built in charger in the generator, but have no way of knowing the charge of the battery before or after charging it off the generator. I was told that if this generator has a 8amp charger that I do not need to buy a regular battery charger to take on our trip. My brother mentioned that he has a tester simular to those old antifreeze testers in which you draw up battery fluid to find the charge of the battery. Wondering if you can buy a meter type device that will show the batteries charge without drawing out battery fluid to test the batteries charge?


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## VonWolfen (May 24, 2004)

There is. I am no expert, but I have pick and shoveled my way to some knowlege. In truth, the hydrometer test (the turkey baster thing that checks specific gravity) and the voltage check really only check the current condition of the battery and not whether it is ready to do its intended work. You can buy a load tester, that is what you need, or you can do it with an old starter. Hook up a car starter to your battery, then hook up your multimeter to the terminals..put on DC and see the charge. It should be between 12 and 12.9 to start off with (fully charged). Crank on the starter for 15 seconds and watch the multimeter.....if it drops below 9.6 volts within 15 seconds...it is time to replace. It is the only way, to my knowlege, that you can test the true condition of a battery. Hope it helps.


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## 12vman (Feb 17, 2004)

You could get one of these and one of these to keep an eye on things..

With the load tester, if you hit the switch and it goes into the red as soon as you hit it, the battery is in need of a charge pronto! Charge until the meter stays in the green with a quick hit of the switch..

With the volt/ohm meter, (set on voltage) with a reading of 11.8 volts, the battery is pretty much dead. (with nothing running from it at the time) IIRC,you were using large marine batteries. Usually they are around 60-65 aHr. reserve. (forget the CCA mumbo-jumbo)

Let's say they are 60aHr. batteries and you have a voltage reading of 11.8 volts. (pretty much dead) You have the ability to charge at an 8 amp charge rate. (charging 1 battery at a time) Take your aHr. rating and add 20%. (12 aHr.) This gives you 72 aHr. to replace in that battery. (the 20% is normal losses) Now, divide the needed amp hours with the amount of charge possible. (72 and 8) It would take around 9 hrs. to recharge your dead battery.

Open Circuit Voltage VS. State of Charge 
12.66V 100% 
12.45V 75% 
12.24V 50% 
12.06V 25% 
11.89V 0% 

Check this place out and learn about batteries..
~Don


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## wy_white_wolf (Oct 14, 2004)

I don't diagree with the voltages that 12vman gives. Just need to clarify that those are the voltages that are after sitting for 4 to 8 after charging or discharge. 

some good toturials on charging batteries

http://www.batteryuniversity.com/partone-13.htm

http://www.powerstream.com/SLA.htm

http://www.solarnavigator.net/battery_charging.htm


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## Jim-mi (May 15, 2002)

You could forget all of the above if you'd put a Tri-Metric in line.
It will tell you what you've put in and what has been taken out.

It would be wise to spend those bucks to keep your batt from a quick death.

period


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## Al. Countryboy (Oct 2, 2004)

To each of you with your help. I am getting ready to check the sites that you mentioned and do some search on a tri-metric in line that was also mentioned. Thanks again.


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## wy_white_wolf (Oct 14, 2004)

Yes Jim-mi he could. But with a low end cost of about $200 he could buy 3 to 4 of the cheap Walmart deep cycles that he plans on running.

A $10 multimeter and a little studying should get him by. In the future if he does get a good set of batteries and a tri-metic than the knowledge will give him the appreciation for what it does.


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## Jim-mi (May 15, 2002)

LOL . . .wolf . . .can't argue with that.

Guess every one needs to kill a batt so as to be able to say....
Opps

Have you checked batt prices lately . . . ??
they will soon be double the 'year ago' price........


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## wy_white_wolf (Oct 14, 2004)

Not lately, but will be looking into some T-105s or L16s here in the next year or 2. I'm sure it's going to make me bawk. A tri-metric is in the works for them.

Actually do you know of any other batteries coming out soon for a mid sized system that might be better?


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## Jim-mi (May 15, 2002)

I don't use trojan's any more. Many neg issues. . .price\distribution\attitude--(we are the best so we charge more for our hallowed name etc.)

U.S. Battery is a good brand....


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