Single big battery v/s 2 batteries in parallel

samhain7 wrote:
Hi everyone. I have a Kirkland Deep Cycle/starting battery.
On the front it says
- FTIMENT Code 14
- Group Size 27DC
- 845 Marine Cranking Amps
- 120 Amp hours

Is it worth it to get a second one? Does anyone have a wiring diagram?
Anyone want to share a sweet set up?

How old is this battery?

Re: Harold Barre's book "Managing 12 Volts" (New Second Edition)

I went and got a copy of the book from my local library.

It has everything you would need to know about 12 volt systems.
Throughout the book he talks about 3 basic examples: Motor coach, travel trailer and sailboat, giving examples in each topic for each of these vehicles.

It contains formulas, checklists, and examples to make it easy for you to calculate your 12v requirements, both for minimal and optimal needs.

In simple layman's terms he starts by explaining basic electricity and electrical principals (voltage, amps, resistance) so that even the novice who is totally unfamiliar with electricity can understand it.

He builds on these basics and leads the reader into the more complex topics and discussions of 12v systems.

He also discusses trouble shooting 12v systems so that you can save yourself some $$ instead of hiring a tech every time you have a problem.

I liked the book so much since it contains so much valuable information that I went and bought a copy.

It is available via Amazon here:

http://www.amazon.com/Managing-12-Volts-Troubleshoot-Electrical/dp/0964738627/ref=sr_1_1?s=books&ie=UTF8&qid=1389967208&sr=1-1&keywords=managing+12+volts

It really comes down to getting more battery life for the dollar with the 6v golf cart batteries and the reason for 6v is to keep the weight down so a person can lift them into place. But neither golf carts or forklifts where these are commonly used have only 2 batteries installed.

With an RV if one cell is bad in one of the 6v batteries you no longer have 12v which is needed to operate any electronic devices including the fridge and the furnace thermostat. If you have 4 batteries then you can afford to lose one and still have 12 volts possible until you can replace the battery with the bad cell.

As a practical matter I use two 12v batteries wired in parallel so if one fails I lose some amps but still have 12 volts. The most we have ever discharged them is 22% so even with one battery that would still take keep it above 50% DOD.

Hi everyone. I have a Kirkland Deep Cycle/starting battery.
On the front it says
- FTIMENT Code 14
- Group Size 27DC
- 845 Marine Cranking Amps
- 120 Amp hours

Is it worth it to get a second one? Does anyone have a wiring diagram?
Anyone want to share a sweet set up?

Steve., when you put two batteries in parallel the best way is like this.

(Ignore periods in the next two lines

Ground|-{Battery1}+
. . . |-{Battery2}+==Fuse and distribution panel and charger

This way you do not worry so much about resistance as it's the best balance you can get. You may reverse 1 and 2 since those are arbitrary by the way.

As someone said: With 2 in parallel there is a CHANCE one may short and take out the other leaving you with nothing.. There are a couple other failure modes. and when I had one short it did not take out the others. as once I removed the shorted cell they all pass tests (load and duration of run on inverter power for house)

So the key word in that phrase is CHANCE.. There is a CHANCE (A good one) that won't happen.

The reason I like a six volt pair is simply cost. Best bang for your buck.

Pulling high loads that would almost make sense. Everything I have read about the batteries we are using would seem to say the opposite, as a battery rated at a 20 hour rate has a higher AH then the same battery at a 10 or 5 hour rate. Pulling 15.4 amps off a 77 AH (5 hour rating) battery will drop it to 50% DOD in 2.5 hours, paralleling two of those same batteries gives them a 10 hour rating of 164 AH (82*2), now they would last 5.32 hours to 50% DOD. Another pair (4 batteries) would give them 356 AH (20 hr rate 89 AH) and last 11.56 hours to 50% DOD.
In a Diesel / Electric sub you are pulling hundreds of amps turning the prop, and depleting the batteries in a matter of hours, and waiting for dark to surface and recharge the batteries.
Even in the big solar systems I have worked with they use 2 volt jars the size on mini fridges, and series / parallel them at 48 volts. Most rv's don't have room for 6 1000AH 2 volt batteries.
Most RV'rs are trying to avoid deep discharges and last several days with a minimum of charge cycles.


Battery Specs

All I know is my battery bank has all 740Ah available. Series/parallel.

Matt, interesting explanation based on some extreme limits.

I agree there will be some circulating currents and some ampacity lost, but it is typically minimal when using batteries of the same type, age, and physical condition.

If battery technologies are mixed, or batteries of differing ages and physical conditions exist, then your extreme limit examples can occur.

In general, and if standard practices are followed, batteries can be connected in parallel without issue.

BFL13 thanks for the info.
My local library has a copy so I will check it out.
Thanks.
Steve.

SKSCCI wrote:
Good Evening Matt!

Thanks for the details.
Here's what I got from your discussion:
1. Buy a single 200AH battery and it will be good until it dies.
2. Buy two 100AH batteries and you will get about 150AH and they will be good until ONE of them dies. When the one dies, depending on how it dies, there is a chance that it has damaged its brother in parallel. So, instead of being able to depend on a backup battery, you may be in just as much trouble if not more so with 2 in parallel.

Some people have spoken about getting 2 6 volt batteries and using them in series for a 12 volt system. Is this situation pretty much the same as far as potential problems as 2 12v in parallel?

Thanks.
Steve.

Steve, Matt is all mixed up on this topic, so listen to the others for now. You can't go wrong with this book to bring you up to speed. Matt should read it too--the author was in the navy if that helps. :)

http://www.bestconverter.com/Books_c_67.html