Charging multiple batteries

[harleyman_1000]

 I am wondering if I can charge more than 1 battery at the same time, with 1 battery charger? If so how?

[Oonrahnjay]

I am wondering if I can charge more than 1 battery at the same time, with 1 battery charger? If so how? 

        I asked a similar question in the past and I was told that the answer is pretty much no (at least in practice).  If one battery is slightly sulfated (and most used batteries usually are), then the imbalance of resistance and charge acceptance means that the two batteries don't charge at the same rate and you end up with one not fully charged; the effect is worse with modern "smart" chargers, which read surface voltage and resistance to know when to "stop charging".  If you're *very* lucky and both batteries have exactly the same charging characteristics, you might get away with it.  But in practice, what it usually results in is one battery chronically lower in charge, with the long-term bad effects that that brings.

        I understood that when I got that answer here a few years ago.  I would like to think that maybe that's too theory-oriented, and maybe in real-life, it would work out pretty much OK (and maybe it would), but I went out and bought a separate $27 Stanley "smart charger" for my start batteries.

        If someone has a way to make this work, I'd be glad to hear it.   

[Seangie]

When we are boondocking somewhere with a 20 amp and we can't run our genny (like a residential neighborhood) Ill charge my house bank (currently 2 batteries) and then charge my starter bank (3 batteries) without seperating them.

I bought all these batteries new at the same time and for the most part it works fine charging them in banks.  I am a 12v system and all my Batts are 12v so it makes it easy to put the negative charger on one post of the end battery in a bank and the positive charger on the positive post of the battery on the other end of the bank. If you have 6v batts in a 12v or 24v configuration or 12v batts in a 24v configuration it may be different. 

Also -  I do notice that sometimes the charger reads whatever the voltage is across all batts in a bank.  A problem with this could be that if one battery is bad then it will keep charging even if the good bat is full (it won't switch to float)

It may not be the "proper" way to charge them but its the way the inverter charges them.  I do suggest charging each battery seperately at least once every 6 months to make sure its healthy and holds the proper charge when done (maybe desulfating once a year?)

-Sean

Fulltiming somewhere in the USA
1984 Eagle 10S
www.herdofturtles.org

[Dave5Cs]

Scott is your bus 12 or 24 Volt.

Mine is 24 volt and I charge on the end of the string with 4, 6 volts in wired series with no problems. They have been on charger for 3 years. Didn't have a working inverter until recently.
I desulfate them every 6 months.

Dave

[gus]

Obviously the bus alt charges all the batts at the same time as does my converter.

However, when I use smart chargers I do them one at a time because I think it does a better job.

[Melbo]

I use a 24 charger to charge my batteries and my inverter / charger charges my batteries when they are all connected.

My battery banks ( start and house ) have been tied together and charged together for almost 10 years now without incident.

I always completely disconnect EVERYTHING (with the exception of the trimetric shunt ) from the batteries when I am not using the bus.

HTH

Melbo

[TomC]

I charge the 4 starting batteries in my truck all together. The only thing is that if they are discharged too much, the charger sometimes think they are bad batteries. Just have to unplug and re plug in the charger to continue. Eventually-they charge up-but can take 2 days with a 20amp charger. Good Luck, TomC

[Oonrahnjay]

...  Mine is 24 volt and I charge on the end of the string with 4, 6 volts in wired series with no problems. They have been on charger for 3 years. Didn't have a working inverter until recently.
I desulfate them every 6 months.      Dave   

         What kind of charger (brand and model #, please) is your charger -- I'm assuming by your post that it's a 24V charger?   Is it a "smart charger/ float charger"?  What's your process to desulfate them?   
         Thanks for the info,   Bruce H   NC   USA

[Oonrahnjay]

I charge the 4 starting batteries in my truck all together. The only thing is that if they are discharged too much, the charger sometimes think they are bad batteries. Just have to unplug and re plug in the charger to continue. Eventually-they charge up-but can take 2 days with a 20amp charger. Good Luck, TomC  

      Two days, interesting.   I run starter and headlights/taillights off my 24v system.  About 2 1/2 years ago, I bought two Type 31 batteries from NAPA.  I almost never run at night so these batteries are used almost entirely for starting the engine (I have a separate 12V alternator for the house batteries).
      I am very careful to switch these batteries off with the master switch when the vehicle isn't actually being used (in fact, if I move it to the wash pit and park it for 15 minutes to wash it, I'll switch the batteries off while it's parked).  I had my bus inside a shop area for about a week before Christmas, then as the Holiday was approaching, I started the engine (50º weather), moved it to its parking place in the storage yard and shut it down and immediately switched off the master.  I was away over Christmas and New Year for almost 3 weeks.  When I came back, I put my little 6 Amp chargers on the start batteries - in less than 10 minutes, they'd gone to "float".



      I attach one charger to each battery, although the batteries are joined together with the jumper.  Since the master is off, there's no current flowing through the batteries.  I think that this separates the batteries and the individual chargers correctly sense the battery state and switch to float properly.  Here's a diagram.


     Am I doing anything wrong?  Are my start batteries really staying "hot" enough so that after 2-3 weeks of being parked, 10 minutes charge at 6 Amp (I don't bother with the 8 Amp "boost" setting on the chargers) is enough bring them up to fully charged/float?

     Thanks for any advice.   BH  NC   USA

[Cary and Don]

We charge our batteries in banks. On the house batteries, each pair of six volt batteries are connected to a bus bar. We have found that this works better than daisy chaining them together. Twice we have taken them apart and charged each battery separate.  Then we swap the two 6 volts in position so that the positive end becomes the negative end. This has worked best for us.  These batteries are eight years old and still working and they were the cheapest batteries we could find, Sam's Club.

Don and Cary 

[Oonrahnjay]

We charge our batteries in banks. On the house batteries, each pair of six volt batteries are connected to a bus bar. ...

    Your house system is 12V, Don?   (Nice performance from your batteries -- you are obviously doing something right!)

[Cary and Don]

Yes, it's 12 volt.  We have a 24volt inverter in the garage. One of these days we plan to switch over.

Don and Cary

[Oonrahnjay]

Yes, it's 12 volt.  We have a 24volt inverter in the garage. One of these days we plan to switch over.    Don and Cary   

     Yeah, me too.   

[harleyman_1000]

My bus is 12 volt. I have 2 start batteries, 2 house batteries, and 2 12 volt batteries wired to run my 24 volt inverter, so I have 2 separate house banks

[Geoff]

My bus is 12 volt. I have 2 start batteries, 2 house batteries, and 2 12 volt batteries wired to run my 24 volt inverter, so I have 2 separate house banks

Scott-- You "USED" to have a 24v interter, but as you recall I took the inverter out and the relays out and hooked up a 12v system since you didn't have a 24v alternator.  I put a new 160amp 12v alternator on your engine while you were here at my shop in Prescott, and all wires to all batteries are hooked up to 12v only.

--Geoff