Battery Question: Combine my batteries?

Unexperienced dry campers experience dead batteries quite often.
Experienced dry campers never experience dead batteries.
We never wonder if our batteries will do what we ask them to do,....we already know what they will do, and don't ask any more from them.

Get a digital readout volt meter, mount it in plain visual sight, learn to read it, then parallel the batteries together.

I can never remember the name of Peukert's law but thankfully Google can.

Look it up for more detail but basically what is says is this.
The slower you discharge a battery the longer AND THEN SOME it lasts.

So, if your one battery lasts say 8 hours, then the pair will last 16 right.. Wrong, more like 20.
And up to a point the slower you recharge them the longer in years they last (So you just cut the recharge rate in half as well).

This is why I do not recommend two independent banks I do recommend a portable "Jump Start" battery for motor homes (In case you need to feed Mr Onan a bit of power so your converter can do the recharge) Been glad I had one on occasion.

Oh, and if you really want to see something

Try a pair of GC-2 Golf car batteries in series (that is basically a 4D battery, 230 amp hours at 12 volts) unles your existing are group 31 or larger you should see improvement.

plus as true deep cycle,, they may last longer in deep cycle service.

Yes, with Peukert Effect you get more AH out of the pair together than using them one at a time.

When you get home, separate them and charge each one to full baseline SG. You can then Float them separately if you have two Float controllers or chargers, or connect them back up and Float them together. Just don't try to recharge them together to 100% as one won't get that high if they are not identical.

While camping it is ok to recharge them together since you will only be doing 50-80s or 50-90s anyway so who cares if one gets to 91% and the other to 89%?

BTW, never heard of Launch and "Retrieve" You "Recover" your aircraft :)

LaunchnRetrieve wrote:
I've never combined them because I've worried I would run them both down and not have a back up.

Don't you have some way of knowing how discharged they are?

And, by running one down then letting it sit discharged, you're hastening the end of its life.

Put them together in parallel. Then add 100 watts of solar and enjoy your days.

Theoretically (Peukert's law) it is the best to tie them together. Ideally they should be same age and size but I have had mixed batteries in the past that gave what they could in terms of available amphours. When dissimilar batteries are used together one will drag the other down as well as having different charging characteristics. Even with those drawbacks two batteries are better than one as long as neither is totally shot.

If you decide to connect them together, 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?

Here is a video of 3 twelve volt batteries that have been wired in an unbalanced manner for 2 years. They have been equalized. The test shows how CCA has been adversely affected.

unbalanced for 2 years

Primary reason to combine when discharging is if you run high loads.

http://en.wikipedia.org/wiki/Peukert%27s_law

If you are not powering an inverter or other high-draw load, you don't gain much.

This is my layout which uses four position BLUE SEA HIGH CURRENT BATTERY SELECTOR switches.



With this arrangement I have enough CONVERTER/CHARGER capacity with the PD9260C to handle all four batteries if selected.

If I was to what you are are doing I would select one, two or all of the batteries with different switch positions.

I too sometimes isolate one bank to run something else and not be in my POPUP Trailer system. i.e. I have two batteries supporting the POPUP Trailer demands and two additional batteries running my two-way radio setup I have which is separate from camping.

I can either charge one, two, or all with the different switch settings. I can also switch two batteries out of the loop and charge them with a second direct connected charger being run from my 2KW Generator if I want to do that.

Just gives me multiple configurations with my battery bank.

These BLUE SEE Battery switches also work out great as a complete BATTERY DISCONNECT if that is needed...

My normal configuration is all four batteries connected to the PD9260C converter/charger unit. This allows me to have 340AHs of battery capacity for the OFF-ROAD POPUP and keeps them all charged the best. It is nice however as circumstances dictate I can switch out any, all, or none batteries in the setup.

Roy Ken

You'll hear a dozen different reasons why keeping them together or separated is better. Seldom is the most pertinent reason to parallel them mentioned..

You have a charger or charging system. When you enable the charger a monster fuel eater starts up. Here is an exaggeration It gets the point across.

Let's say one 6 cell battery drops to a 12 amp charge rate rather than a 35 amp charge rate during the peak of it's hunger. Running a generator to get a piddly 12-amps is horrible to think about, right?
But what would happen if there were four batteries instead of one?

48-amps is not so piddly, is it? And an amp hour is an amp hour no matter which way the bread is sliced.