12 volt battery questions?

[D.J.]

A guy I work with has a boat and uses two 12 volt batteries that are hooked up parallel to run lights for bowfishing and wants to know what the best way to hook up the posts to charge the batteries when they need topping off. We were talking and I suggested he unhook each battery and charge independantly when charging. Also whats the best way to hook the cables when attaching positive bat #1 to positive bat #2 then to appliance and from negative appliance to Bat # 2 then to bat #1? I hopeyou aregetting what the question is I'm typing. Thanks in advance for your responses. I'll try to include a picture of a drawing. Thanks D.J. "img[http://1273016723]/img

 

[Stuart in MN]

As long as the two batteries are the same type and size, and they're both in good condition, they can be charged in parallel. You don't have to disconnect them and charge them separately.

 

[rockwithjason]

agreed

 

[Vicegrip]

Both need to be in identical condition and age to fully and reliably charge while connected. If there is any inequality in the cells the charge can be uneven between the battery and even between the cells. This can happen while charging a single battery as well. Some of the better modern battery chargers have an equalization mode to help deal with uneven charging rates between cells. Will it work OK? Yes, if they are the same. Is it the best method? No, unless you are using a charger that has the amp cap and mode to equalize after charging.

 

[theoldwizard1]

Both need to be in identical condition and age to fully and reliably charge while connected. If there is any inequality in the cells the charge can be uneven between the battery and even between the cells. This can happen while charging a single battery as well. Some of the better modern battery chargers have an equalization mode to help deal with uneven charging rates between cells. Will it work OK? Yes, if they are the same. Is it the best method? No, unless you are using a charger that has the amp cap and mode to equalize after charging.

+1

In a perfect world it would be fine. The world is not perfect.

One dead cell could possibly kill both batteries. They make a marine battery combiner switch. Electrically disconnects the batteries from each other when not in use.

 

[gatchel]

Both need to be in identical condition and age to fully and reliably charge while connected. If there is any inequality in the cells the charge can be uneven between the battery and even between the cells. This can happen while charging a single battery as well. Some of the better modern battery chargers have an equalization mode to help deal with uneven charging rates between cells. Will it work OK? Yes, if they are the same. Is it the best method? No, unless you are using a charger that has the amp cap and mode to equalize after charging.

+2

I would separate them to charge them. The more you series/parallel individual battery cells the more potential for problems. Will you have problems, probably not. Charging them separately will limit the possibilities for issues to arise.

 

[nehog]

As long as they are both good, and roughly identical, just charge in parallel... Diesel trucks almost always have two parallel 12v batteries, charge in parallel, and with no problems. Use a reasonably decent charger and you'll be OK. If one battery is defective (has a bad cell) it will discharge the second battery however, this is an easy to diagnose problem...)

(These rules don't apply to 12V batteries connected in series to get 24 volts, however...)

 

[theoldwizard1]

If one battery is defective (has a bad cell) it will discharge the second battery however, this is an easy to diagnose problem...)

So how is it easy to diagnosis when both batteries have no charge ?

 

[kbs2244]

Have him go to the local big box fishing store and get a twin battery charger.
They are cheap these days.
The are basically 2 chargers in one housing and with one 110 line to feed them.
They are isolated from each other.
They are designed so he can hook it up permanently to both batteries and just plug it in when he comes home.
They even make 3 battery ones so he can charge his motor starting battery if he worries about it. (I feel that is over kill in most cases.)

One trick I learned from the battery mfg. rep that came to train us was that batteries will develop what he called a “false charge” when being charged.
Is at its worst with high amp chargers.
This false charge will trip the charger to go into maintain mode before the battery is actually fully charged.
The fix?
Plug in the charger when you first get home, go in and shower, have dinner, watch some TV.
Then before you go to bed just unplug and replug in the charger.
Unplugging the charger will reset the “fully charged” sensor and it will start charging again.

 

[bochnak]

Definitely hook up a battery switch like this:

http://www.google.com/products/cata...=X&ei=2N-UTfXtJ-aU0QH0qYmGDA&ved=0CDMQ8wIwAQ#

 

[nehog]

So how is it easy to diagnosis when both batteries have no charge ?

Charge both batteries fully. Disconnect the strap that connects the two, and after 24 hours measure open terminal voltage. One will be much (about 1.5 volts) lower than the other--it is the bad battery.

Personally (well, I've been in this business (electronics and electrical engineering) for years) I think that some people here are making this much more complex than it really is.

 

[2LTim]

Something to remember guys, the rule of thumb for charging ALL automotive type batteries: Charge for a minimum of 8 hours, at a maximun rate of 5 amps (per battery). If you are charging 4 batteries connected in parrallel, your max. rate would be 20 amps. I know, some of you have buddies that are battery reps who say to hit them with 75 amps for the first half hour. This will kill a good battery and require you to purchase a new one, hopefully from your "Friend." The manufactures of batteries will tell you, "Minimum 8 hrs, Max 5 amps."

 

[holdover]

One of the best tools I purchased is a battery load tester. I live on a farm and have about 10 batteries in tractors, vehicles, lawn mowers etc. The load tester tells battery condition under load. Once you use one you will find that no two batteries are the same, even if same amp rating and age. With that said I do not charge in parallel.

 

[rockwithjason]

i ran across this in my daily travels. you may want to take a look at it

http://www.powerwerx.com/emergency-vehicle/battery-integrator.html