Car Battery Charging Testing Questions

traderfjp · Post by **traderfjp** » Thu. Sep. 25, 2008 8:42 pm

Hi,

I have an electronic battery charger. I can test for voltage but it doesn't tell me how full the battery is? Is there something I can buy that will tell me how fully charged a battery is? I'm setting up a battery backup using 2 marine batteries and will need to charge them periodically. I also need to wire them together for 24 volts. I can charge them together or do I need to charge each one individually?

http://www.amazon.com/Vector-VEC1089ABD15-Charge- ... 36&sr=1-13

Thanks

Freddy · Post by **Freddy** » Thu. Sep. 25, 2008 9:00 pm

That charger will do a good job. Just let it do it's thing. If connected parrellel (12V)you can charge both at once. It'll just think it's a huge battery. If in series (24V), you'll have to charge them seperatly. You can leave them wired together, just do one at a time. If the batteries are not used you could charge them once every two weeks & be fine, maybe 3 but I wouldn't go 4.

Voltage: a fully charged battery will be 12.6 to 12.8 volts. It's concidered drained at 11.6V. There's a trick though, they get a "surface charge" that makes them read high. If you are using voltage to tell if it's full you have to take the surface charge off it by "turning on the headlights" for 3 minutes.

I wouldn't even worry about it. The charger will tell you when they're charged.

Rick 386 · Post by **Rick 386** » Thu. Sep. 25, 2008 9:10 pm

Trader,

Years ago we used a battery hygrometer to test the cells. The amount of floating balls determined the state of the charge left in the battery. Of course that was when you could get access to the individual cells through the caps. If you buy the type batteries that have removeable caps, you are in business.

That charger you listed supposedly has the capability to tell you when the batteries are full. If I read the model correctly, it will charge at 3 different rates 15 a, 10a and 2a.

Are you buying deep cylcle or regular batteries ????? IIRC Deep cycle need a slower charging rate. But last longer on the discharge side.

I don't think you will be able to charge them wired as 24 volts. You will probably have to charge each one individually. If you are going to keep them hooked up in series, you may want to look into a bass boat charger. A lot of the bass boats use a 24v electric trolling motor.

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Rick

gambler · Post by **gambler** » Thu. Sep. 25, 2008 9:20 pm

traderfjp wrote:Is there something I can buy that will tell me how fully charged a battery is?

Go to the auto parts store and buy a hydrometer. Kind of a pain to measure each cell but is accurate and cheap. Or you could spend more money and get a battery tester that you just clamp to the posts. Real easy but don't know how much they cost. Or hook your charger to it and see how much current the battery is drawing. As the battery gets charged it draws less and less current. I think they even make a battery gauge for marine apts. so you don't have to remove the battery from the boat to check.

Bulldogr6 · Post by **Bulldogr6** » Thu. Sep. 25, 2008 9:22 pm

You need to load test them, use something like this.

cheapest one I came across with a quick search
**Broken Link(s) Removed**
Higher load test
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Just find and buy a 24v charger/tender and your good to go.

traderfjp · Post by **traderfjp** » Thu. Sep. 25, 2008 9:34 pm

Thanks. I tried the charger I have and a Volt meter both read that one battery was 12.6 and the other was 12.7. Do I still need a battery tester? I guess I shoud have bought a 24v charger so I could leave them hooked up and charge them together. I may still buy one. The batteries have caps so I could use a hydrometer and they are marine batteries.

CoalHeat · Post by **CoalHeat** » Thu. Sep. 25, 2008 9:36 pm

Years ago we used a battery hygrometer to test the cells. The amount of floating balls determined the state of the charge left in the battery.

Yes, to do this you need a battery that has removable caps on the cells. I used to have a hydrometer that had a float for measuring a battery's specific gravity and it had a thermometer in it for adjusting the reading according to ambient temperature. It has long since succumbed to dry rot.

https://en.wikipedia.org/wiki/Hydrometer

Measuring the specific gravity is a true indication of the battery's state of charge, as well as a way to discover a weak cell.

I know there are chargers out there somewhere that will automatically read the battery's condition and charge it accordingly, you leave it connected all the time.

traderfjp · Post by **traderfjp** » Thu. Sep. 25, 2008 9:43 pm

Time to buy a hydrometer. I think we all had one at one time or another.

gambler · Post by **gambler** » Thu. Sep. 25, 2008 10:34 pm

traderfjp wrote:Time to buy a hydrometer. I think we all had one at one time or another.

And like Wood'nCoal said all of the rubber bulbs have long since succumbed to dry rot.

Post by **coaledsweat** » Thu. Sep. 25, 2008 10:37 pm

So that's why grandma needs a new turkey baster every few years even though she cooks one a year.

Rick 386 · Post by **Rick 386** » Fri. Sep. 26, 2008 9:15 am

Yeah,

I realized after I posted that it should have read HYDROMETER.

I was tired and figured a little Norm Crosby terminology would still get the point across. Besides I was sweating working late, hence the reference to humidity.

I'll try to be more careful the next time........................

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Rick

Dallas · Post by **Dallas** » Fri. Sep. 26, 2008 9:50 am

I would think, rather than charger(s), you would be better off with "battery maintainer(s)". These can be left connected all the time and will maintain the charge, without over charging. I keep one on my Jeep all the time through the winter.

WNY · Post by **WNY** » Fri. Sep. 26, 2008 10:04 am

Good link...

http://www.windsun.com/Batteries/Battery_FAQ.htm# ... 0Batteries

Also, I would go with a good deep cycle type battery, Car Batteries are good for Starting, and have HIGH initial output, but quick discharge, you want something that will discharge slowly.

orvis · Post by **orvis** » Fri. Sep. 26, 2008 10:55 am

I tried the charger I have and a Volt meter both read that one battery was 12.6 and the other was 12.7. Do I still need a battery tester? I guess I shoud have bought a 24v charger so I could leave them hooked up and charge them together. I may still buy one. The batteries have caps so I could use a hydrometer and they are marine batteries.

You will get better performance from the bats longterm if you charge them in parallel, even though it is a pain in the but. Here is why: A battery is made of seperate cells, in the case of a 12 volt battery there are 6 cells of nominal 2 volts each. Each cell has a slightly different behaviour in how much voltage it puts out as it charges. So for example you might have 5 cells that are charged high and one is a little low, but they still add up to the 12 volts. Your charger thinks they are done and shuts off. The more cells you string together the worse this problem gets, and you end up with what is called cell imbalance.