Battery questions

[phishheadmi]

I have a couple quick questions about my battery use.

We have a five night camping trip coming up and won't have shore power available. I have two group 24 batteries...one is about a year old, one is about two years old. The newer one seems to charge and hold to 12.6V the older gets to about 12.45. Would I be better off wiring them together in parallel, or using them individually, one at a time? I'd like to wire them together, but seem to recall reading somewhere that it only worked well if both batteries were identical.


Next, I have a Honda eu1000i generator that I don't want to run much, but can use to charge the batteries if necessary. I do have the optional charging cable for the gene, is it more efficient to use that, or plug in the shore power and charge through the tt's electrical system?

[phishheadmi]

Thanks for the advice everyone, gives me a good deal to ponder. Unfortunately, I don't have time in the two days before our camping trip to do much of what has been suggested. I think I'm just going to roll with what I have and use the generator when I need to. Sometime down the road I'll look into investing in a pair of new batteries, charger, etc. Might as well just add a Honda eu3000 to the list as well 😉

[pianotuna]

Hi,

You could use the better one to 12.45 volts and then switch to a balanced wiring parallel configuration.

Or you could *work* on the weaker battery doing reconditioning and equalizing until the specific gravity of both batteries is the same.

Voltage is generally a poor indicator of state of charge.

[Shadow_Catcher]

I will reinforce run separately as the weaker will pull down the stronger. Invest in a battery monitor Victron or Trimetric it is the only way to accurately know the battery(s) state of charge.

[westend]

From reading between the lines on your battery use, I'd suggest to buy two new 6v GC2 batteries and hook them up with fresh wire and new connectors. The 6V batteries will be more tolerant of your use and will last longer than another pair of Walmart Grp 24's. The 6V are about the same price, if bought at a discount outlet like Costco or Sam's.

After the new batteries are in, you should look at your charging regimen and figure out why you are not getting a full charge to the batteries. Usually, an owner drives a few hundred miles back from the campgrounds and calls it a day without knowing, fully, what state of charge his battery is at. The battery may be disconnected or it may be allowed to run to nothing from the parasitic loads and recharged when another use is anticipated. Using two batteries and changing them out when one gets low, only adds complexity.

You could try to equalize both of the Grp 24 batteries you have and then put them on a trickle charger for a few days. That may get some more use out of them but batteries are kind of like elephants, they have a long memory.

AFAIK, the 12V charger output of a Honda 1000 is about 8 amps. Your stock converter should be better than that by a factor of 4X.

[gbopp]

Read this, it may answer some of your questions.

The 12 Volt Side of Life

[tenbear]

phishheadmi wrote:
Thanks for the info. If I were to use them separately, at what reading would I want to stop using one battery and switch to the other?

As a rule you should not draw a battery down lower than 50%. That corresponds to a voltage of 12.06v.

[bigcitypopo]

Pianotuna has it right... Pull them both from rig... Run each thru a desulfate/recondition mode then charge. Let sit... Read voltage...

Then I'd wiire them together as depicted above and run through a charge cycle at max AMP... I use a black and decker vec1093dbd... By far the best I've owned...

[Artum_Snowbird]

I would use the weaker one first. You will have a good idea how long the better one will last then.

With your voltmeter, and when you are not using loads for 30 minutes or so (like pumps or fridges or lights), measure and record the battery voltage and hours used. It's very useful to have a chart and then you will be able to judge how long it will take to use up each .1 of a volt. I use up about .15 from two 6V batteries each day, so get 4 days from 12.6 to 12.0

Plug your camper into the generator through a 15 Amp dogleg, and let the converter charge the battery.

[phishheadmi]

Also thank you pianotuna. That's the way I had planned to wire the two batteries. I'm sure I'm over thinking this, I'm running all led lights and an efficient water pump which, along with a small draw from the fridge is really all I'll be running. We've gone three or four days on a single battery with no problem. I like wiring them together because it saves switching them around while we're there.

[phishheadmi]

Thanks for the info. If I were to use them separately, at what reading would I want to stop using one battery and switch to the other?

I'll have to look into some more detailed specs on my generator 12v line as well as the converter charger.

[pianotuna]

Hi,

Because of the Peukert effect, batteries wired in a balanced manner will allow more total amp-hours than using them individually.

It would be best to equalize both batteries individually to get them up to the greatest possible capacity.

Recharging from the generator should be done with the existing converter, if it is a modern three stage. Additional chargers can be "piggy backed" up to the limits of what the generator can power watt wise.

The output from the EU1000 is unregulated, and limited to only about 8 amps. That is a poor way to recharge a battery bank.


This is what is balanced and best for twin twelve volt batteries.



As it often doesn't cost a dime more to do this, I think it is worth the trouble.

If you wish to understand the "why" surf here:

correctly interconnecting multiple twelve volt batteries

Others may say it doesn't matter--but unless there is a compelling reason to not optimize charging and discharging why not do it the best possible way?

[tatest]

That much difference in age and condition, I would use them separately, because the battery at 12.6 will give up charge into the weaker one, without it actually storing any more energy.

I have a pair, wired in parallel when installed new, but usually one gets weaker first, and when I detect that happening, I'll split off the bad one and use the good one, until I can replace both.

At least twice a season, I'll disconnect the batteries and separate them, to charge them each with an external charger.

What do you know about the 12V line from your generator? Is it a smart multistage charger? Is it rated for more output than your converter charger? Usually the fastest way to charge from a recreational generator is to use the 120V output to feed a smart charger with peak output amperage rating number that is at least 10% and up to 20%, of the number that is your amp-hour rating on the battery.