dual batteries - do they have to have the same specs?

[lostgravity]

Hi,

My name is David, I'm new here. I've got a 2001 Tacoma that I'm planning to put an auxiliary battery in, with a battery isolator to make sure I don't drain the main one when running an inverter without the engine running.

I searched for this in the forum, but couldn't find it discussed, so:

If you put an isolator between the batteries, does it matter at all whether they have similar specs (like, do they both have to be deep-cycling, same Ah, etc.)? For example, on Optima's FAQ it says that they should be identical - but I'm wondering whether this is only the case if you run them in a parallel or serial configuration...?

Thanks,
David

 

[dustboy]

First off, avoid the Optima, they have fallen into disfavor around here. The Sears DieHard Platinum seems to be the battery of choice.

 

[mhiscox]

Welcome to the forum, David.

If the batteries were truly isolated, in the sense of them not charging off the same source, they would not have to be the same. This is how it is on trucks like mine that have separate "engine" and "house" batteries.

But if the two batteries will charge from the truck alternator at the same time, the batteries should have charging characteristics that are as similar as possible. This is your situation, I believe; your "isolator" serves just to prevent current flow between the stronger of the aux battery and main engine battery to the weaker one, right?

However, it turns out that flooded cell batteries (as you probably have for the engine start battery) and AGM (absorbed glass mat) batteries like the Optimas have charging characteristics that are sufficiently similar that they'll function together as a "close enough" sort of thing. Not as good as matching batteries, but it will work. Avoid a gel cell battery; they are not sufficiently similar. (Avoiding them should be easy, because there aren't many gel cells around these days).

FWIW, I agree that the Optimas have fallen out of favor on the forums, and that they perhaps aren't the very best. I also agree that the Platinum Die Hard (which appears to be the same as the equivalent Odyssey) seems the hot battery of the day. However, if my local Costco is anything to go by, the Optimas might still be the most cost-effective choice. Last I looked, Optima yellow tops were $120, IIRC, which seems very good value to me given that you have a decent warranty to protect against lemons.

 

[Abel Villesca]

Welcome David! :iagree:

 

[mrchips]

I have 2 Optima Yellow tops in my Jeep, and they work just great, run a ARB fridge off both and a winch and have not had any problems. The one is 2.5 years old and still running strong.

 

[craig333]

Since I can get optima's for 99$ thats what I run, but if that goes away I'll go with the sears batt. I'm sure balanced batteries are optimal, but my personal experience says its not big deal.

 

[ExpoMike]

Optima's might seem like a "great" price value but what is the value when you are out in the middle of nowhere and that Optima is dead. I was lucky and my yellow top died the day before we where leaving on a trip. Had to rush to the place I bought it for a replacement under warranty, which was a PITA.

Currently have a Platinum now and have been very happy with it. Looking at a smaller Odyssey as a "house" battery.

 

[lostgravity]

Thank you, guys, I appreciate the input!

I guess I'll go with a Platinum PM-1 as the aux battery... the primary one under the hood is actually a smaller, yellow-top Optima...

 

[ldivinag]

back in the old days of my car stereo competing thingee...

it was important to get the same batteries off the same pallet to get it as close as possible from one to the other. in fact, checking serial numbers was another thing to do...

 

[tremors834]

I've been running a Regular Sears Diehard as the main (starting) battery and a Diehard Platnium AGM battery (NON Deep Cycle) as the AUX battery for almost 2 years now with out issue.
The batteries are seperated by a solenoid and are only connected to each other when the truck is running/charging.
I was always under the impression that as long as your not charging a Deep Cycle and a Non-Deep Cycle from the same source you'll be fine.
Gene