SIMPLE QUESTION: seeking simple and correct answer

[tx2sturgis]

They gotta have same birthday to play well together, or one picks on another, or so they said 

I wasn't addressing battery lifespan (nowhere in the OP question is that asked) I was only answering the OP question about connecting the battery and the possible 'frying' of something. 

And by the way, OTR trucks generally have 4 batteries in parallel and it is very common to replace one if it goes bad which can happen for a variety of reasons. 

Others here may argue that an older battery will tend to die sooner, and take the new, good battery with it. 

I have seen exactly the opposite in a lifetime of heavy duty use in the trucking industry:

The new GOOD battery EXTENDS the usable life of the older (but still good) batteries it is hooked up to. It shares the loads placed on the entire bank.

Again, this all assumes the batteries are healthy. I did not and would not say that putting a new battery in parallel with a bad, weak, abused, very old, or sulfated battery is a good idea. 

The OP question states the first battery was installed at the van build (presumably this past November)...and we can assume it is in good shape and that it is not 'old' by any definition.

If she had said it was 4 years old and had been discharged below 50% every day for the last 2 years, then that is a different situation entirely. I would not parallel a new, fresh, expensive battery with that older one...as the others point out, it's NOT a good idea.

 

[Weight]

You should have no problem connecting two of the same type batteries together. Use nice heavy wires between the batteries positive to positive, negative to negative. As many have posted above. Here is an instructional about wiring batteries.;; http://www.smartgauge.co.uk/batt_con.html Electrons do the same thing in the USA as in the UK. I use method 3 with positive and negative bus bars.
The group of cells connected together as a bank, is defined as a battery. The battery will be averaged down by it's weakest cell. We can group any quality or quantity of cells together if we can except the FACT that the overall effect will be a average weaker battery due to the weaker cell. Your money, do it your way. I have never had to buy a group of batteries that were manufactured in different months let alone different years.
Maybe a unknown manufacturer of some very cheapest solar controller makes one that "fry's itself if the panels are connected before the battery", but I bet we can't find one. Those instructions are for large arrays of panels that have a potential high voltage and many amperes. For the small systems we mount on a van or trailer there is no problem if the battery is disconnected a few minutes, or even hours, while the panels are connected. If you are afraid of small sparks, cover the panels with a blanket.

 

[John61CT]

Yes if everything else is the same, an age difference of a few months - if the older ones haven't been mistreated - will have a minimal overall impact.

However an abused battery can lose 30-50% of its capacity in that time - if unknown, judging relative State of Health requires a 20-hour load test - if the abusive owner is now reforming their ways, better to start with a fresh bank.

And in other cases, even mix & match different models, we're not talking frying anything unless actually damaged batts are involved, the downsides just relate to overall ROI due to compromised longevity.

All this assumes deep cycling use cases and decent batteries, cranking batts and usage have little relevance.

Examples:

If just one $500 battery out of a $3000 set expected to last a decade has failed in the first year, I would only replace the whole set if I could get over $2000 for the good ones.

If wanting to add another $200 batt to an existing single one that is likely to only last two more years, I'd buy two new ones. If I can't sell or repurpose the old one, give it away or use for a core charge.

 

[John61CT]

> Maybe a unknown manufacturer of some very cheapest solar controller makes one that "fry's itself if the panels are connected before the battery", but I bet we can't find one. Those instructions are for large arrays of panels that have a potential high voltage and many amperes. For the small systems we mount on a van or trailer there is no problem if the battery is disconnected a few minutes, or even hours, while the panels are connected.

Sorry that's just irresponsible - read your manuals people!

I would happily take chances with a cheap SC but not an expensive one, if the instruction clearly state to disable panels before disconnecting the battery that should be followed every time no matter how briefly, no matter how small the system.

Some damage does not show, just accumulates over time, and likely won't be covered by warranty.

 

[JD GUMBEE]

Yes if everything else is the same, an age difference of a few months - if the older ones haven't been mistreated - will have a minimal overall impact.

 
Precisely what I was trying to point out from the get-go.

 

[Wabbit]

Dear Friends,

Do you have a simple answer that I can understand and follow as to how to install the second battery...

Yes, find someone that you trust knows what they are doing and have them do it. Are you near Ehrenberg? I am if ya want someone to come over and look at it. Best of luck!

 

[JD GUMBEE]

SO CLOUD WOMAN,
To review here...

Since your battery is not even a year old and you have not ruined it, you CAN add the second cell without worrying about it.
If your system does not have a disconnect switch, that shuts the batteries off from the entire system, GET ONE PUT ON AT ONCE.
(It is, one of the most basic safety items, second only to proper fusing.)

You can do it with inexpensive items similar to those below. If you use an inexpensive switch like this, I suggest leaving one "key" in the switch.

https://www.amazon.com/Gauge-Copper...2&keywords=battery+4+gauge+lug+wire+12+inches
^^^For connecting the two batteries together.^^^^

https://www.amazon.com/Camco-47453-...3&keywords=battery+4+gauge+lug+wire+12+inches
^^^Jumper for switch install^^^


https://www.amazon.com/VANJING-Batt...92&sr=8-11&keywords=battery+disconnect+switch
^^^For disconnecting the batts from the system. ^^^


Best of luck to you.

 

[Trebor English]

If your system does not have a disconnect switch, that shuts the batteries off from the entire system, GET ONE PUT ON AT ONCE.

But before you disconnect the battery from the charge controller the solar panel should be covered or disconnected from the charge controller.  That's the chronological order question from the original post.

 

[Technomad]

Just a general recommendation, since people keep saying “connect the batteries together”... a better approach is that have two busbars, a positive and a negative one. Get cables from the batteries to the busbars that are equal size and length for all the batteries. Connect the batteries to the busbars and the busbars to the system.

In fact, even better is to have a battery disconnect switch between the positive busbar and the load (which can be distributed with another busbar since it often becomes a common attachment point as you add accessories.)


The reason for this is similar to the arguments for using same type and size batteries— to keep the resistances the same so you don’t inadvertently draw one down a lot and the other a little.