choosing a second battery

Lets make this simple. Here is the current set-up in my '99 Ford Taurus:


Amp is Kicker ZX2500.1 (2500 rms). 1/0 gauge power/ground wire. Blue is power wire in the picture, black is ground wire. The yellow optima: D34/78. The battery isolator under the hood: Stinger SGP32.

Also - Big 3 + HO Alternator are in. (Well only 2/3 at the moment for Big Three)

A few questions. I have a friend who says my yellow optima isn't enough. He recommends a Duralast Marine Battery in place of the optima. This one specifically (part number 27DP-DL): https://tinyurl.com/26a424s

His reasoning: it has an amp hour rating of 115. My optima is rated at 55 amp hours. The marine battery seems better in every category, and is less than half the price of the optima.

Specs for the optima: https://tinyurl.com/28ucayp

So, is he right and was I just silly for buying the optima? The only advantage I see with my optima is that a) top and side post terminals (although the top aren't being used) and b) it is smaller and easier to mount in my trunk.

And hypothetically, lets just say I wanted to add another yellow optima of the same kind to the diagram above. How would I go about wiring that?

The Kicker amp may be getting replaced by a bigger amp (at least 3000+ rms), so that is why I'm looking to get more power.

Forgot to mention if it wasn't clear: the Duralast battery in my diagram just represents my starting battery under the hood. I just found that picture so that is not my exact one, mine is nothing too tremendous or special.

To quote Optima's eCare Manager OptimaJim from mp3car.com, you can parallel Optima batteries.   
If you read JMelton elsewhere on this site, people even parallel un-matched batteries "all the time".
Neither above provided evidence nor data to support their claims.

If you read people like me, we agree with the above and add that the batteries will fail quicker and when one fails, both do (unless you have complex monitoring etc).
This is supported by simple risk or reliability analysis. Also numerous reports by various authorities, and people's experiences - eg The Official Dual Battery Thread (MasterCraft).

A few battery threads on this site put doubts against Optima's (recent?) quality. Others don't.
Locally is seems Optima rarely (if ever?) services warranty claims - the buyer has to prove it is NOT their installation's fault (ha ha bluddy ha - Deja Vu!). I have heard the same said of Odyssey.


For audio system, the second battery is usually used instead of a capacitor. Hence it is "next" to the amp, and will be of low ESR type and need not be a deep-cycle type.

If the battery is intended to provide added reserve time, then a bigger battery is used; probably a deep cycle type.

If the batteries are internal, they must be sealed (AGM or Gel) unless in a vented enclosure.


Whenever your alternator is unable to supply the current drawn by its loads, its output voltage will fall from (say) 13.8-14.4V, thru the battery(s) "surface charge" capacity to below the battery's fully-charged Open Circuit voltage of ~12.7V - ie, the battery will also supply the load.

The battery will eventually flatten if its discharge is not replaced (ie, recharged).
The time this takes depends on load, alternator & battery capacities.   


Voltage drops from the alternator to the amp will reduce the voltage at the amp and its battery.
If the battery is less than fully charged, it will have a higher ESR (which may make capacitors seem more attractive if you believe their hype).
The lower the current, the lesser the voltage drop. (Hence the distant audio battery should fully recharge from a (say) 14.4V alternator given the chance to do so.)


Hopefully the above enable you to choose what suits your requirement.


FWIW:....
Isn't higher AH capacity & lower price desirable? Or is ESR important? If so, will that battery remain fully charged? If so, then reserve time is not important.
Systems can be set up to maintain 14.4V at the amp & battery.
Multiple parallel batteries can be switched by cascading relays from the first battery isolator.
If a charge lamp exists, then usually plain relays (contactors) can be used to isolate batteries cheaply.
If no charge lamp exists, then a less desirable or more complex & costly voltage sensing switch or battery isolator is required, but that can then control other cheaper relays for more batteries.
Isolation of all paralleled batteries overcomes any issues (perceived or otherwise) of whether batteries can be paralleled. It also enables non-matched batteries to be paralleled.
(Isolation in this context means "except when charging". It doesn't exclude "paralleling when required".)

PS - is it strange that people never thought to use the charge lamp circuit? F.ex - in the aforementioned MasterCraft Official Dual Battery Thread, wouldn't that overcome many concerns?
Instead of connecting the relay to a switch or IGN or ACC, merely connect it to D+ or L of the alternator(?).

The dual battery post to end all posts.

This should be stickyd.

To the OP, the diagram is perfectly clear and 99% better than most. I think folks will always get better support if they put a little effort in to their request.

Perhaps you would take the time to briefly explain your process in a new thread for others? I really prefer this to trying to understand 18 run-on sentences with no punctuation or regard for grammar.

*disclaimer - this post is not spell checked :D *

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I know just enough to be dangerous. VERY dangerous.

i would rather upgrade the alternator then get into the multiple battery issue.  a little more expensive, but more usable current.  dual batteries are good if you plan to listen to the system with the car not running for long periods of time.

anonymous1 wrote:

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The dual battery post to end all posts. This should be stickyd.

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I presume that's humour? It is more of the same 'ol same 'ol. It has the usual issues and experience, but misses the available solutions. (But it is 2005 vintage and tends not to progress...)

nismo542 wrote:

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i would rather upgrade the alternator ... but ...dual batteries are good ... for long periods of time.

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Like I keep writing - there is no "best" solution - it is situation dependent.
EG - why change alternator if you merely want a guaranteed starting battery?   

But I tend to agree, for big systems, Big-3 then big alternator are FIRST. To use a bigger or second battery INSTEAD of a bigger alternator is usually flawed logic or knowledge (but not always).