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2004 Forester XT
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Discussion Starter · #1 ·
Hi;
I own a 2004 Forester XT. I need to replace the battery (which is only the 2nd one the vehicle has had).
I am considering an AGM battery, but am not sure whether this vehicle's charging system is suitable for AGM.
Then there is the problem of fit. Would an AGM battery fit my car?

The only reason I am considering an AGM is that I want to run ham radio equipment in the car with the engine off, and have been informed that AGM technology may be more suitable for this use.

Thanks for your help

FW
 

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2007 Forester Sports XT 4EAT
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Discussion Starter · #3 · (Edited)
I checked AutoZone.com and found the Optima Yellow Top for my vehicle. It's about 2x the cost of the standard battery.
I'm not sure I want to spend so much on a battery - especially considering the age of my vehicle. I still need to research this a bit further.

Edit: I am comparing the Optima Yellow Top D35 to the Bosch Platinum Series AGM, which is on sale at PepBoys for $124 (reduced from $189).
Both are AGM, but the Optima Yellow Top is circular mats compared to flat plates. From what I have been reading, the circular construction is superior. That said, what is the end result?

Will the Optima last longer, and deliver more power than the Bosch?
Considering that my car sits for extended periods in the (unheated) garage, and what I have read about AGM compared to Flooded, I am better off with the AGM battery. But am I justified to spend 2x the money on the Optima Yellow Top?

One important factor is this:
Will the Optima deliver enough extra power so that I can run my ham radio transceiver (with the engine off) for longer periods without draining the battery?
This radio has the following specs:

Full (100W) transmit: 22A
Receive (max with signal present): 1.5A

I am assuming that, because both of these batteries are specified to fit my car, that they will charge properly in the car with the stock alternator.
 

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2007 Forester Sports XT 4EAT
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To be completely honest, you'd be just fine going with the highest capacity conventional wet battery that will fit. The main advantage of the AGM battery is that they don't leak, with very little gasing. Specifically with the Optima Yellow top, it's a deep cycle battery... meaning it can be "flat lined"... fully discharged & it will fully recharge. A non-deep cycle battery can't do that.

As to alternator & charging. An AGM battery will work with the standard alternator output, but that's not optimal, as they're designed for a higher charge voltage. That's why we installed the Alternator Diode MOD.

If it was me, I'd go with a second battery just for the transceiver. That way when the battery is depleted, you can start the vehicle with the main battery.

As to pricing. I found "killer deals" on Amazon with free shipping when I purchased our Optima Yellow top batteries. :wink:

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
 

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'21 ISM Crosstrek Limited
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As to alternator & charging. An AGM battery will work with the standard alternator output, but that's not optimal, as they're designed for a higher charge voltage.
While my FXT's battery is doing well at just over a year old, I've been considering a better one given past experience, and with winter on the doorstep.

I monitor my vehicle's voltage constantly... it's the display I have as primary on my radar detector. It is mostly at 14.3v, lowering to the 13s after enough running time, but always 14+ at startup.... which is the point of my post and your quote: how much voltage does an AGM battery require for its "higher charge voltage"??
 

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2004 Forester 2.5X Automatic
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I recently got a good deal on Duracell's AGM battery at Sam's Club. Don't know if it's nearly as good as some of the other AGM's out there like Odyssey, and Optima, but at $140 it was only a little more than a flooded cell battery in the same size. It has done well at low temps so far, but almost any brand new battery would, I suppose.
 

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Discussion Starter · #7 ·
I decided on the Bosch Platinum Series AGM from PepBoys. They offered an on-line coupon worth $66, which was only good through today. So the battery cost me $124 plus applicable taxes. I am getting free installation; and while I think just about anyone with any experience at all can install a battery, I will check it thoroughly once I get home.

I think the battery has a 48 month warranty, but so did my last battery, which held out for 7 years!

I once worked with a guy who claimed that all batteries of any particular brand/type were the same except for the warranty. I think he was thinking specifically about Sears, because I was a big fan of the Die-Hard battery. I used to spend the money to get the 60 month battery, and he insisted I was wasting my money.
 

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2007 Lexus GX470
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I bought this because I didn't feel comfortable doing the diode mod myself. Several of the guys on the Legacy forum have been running this for years with their AGM batteries without any issues.

https://www.ebay.com/itm/Alternator...e=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649

https://www.hkbelect.com/product/156-mk3-mini-blade-75a-electronic-fuse-version-2011/

I put an AGM battery in my FXT about a year ago and killed it in no less than 11 months. Then I learned of this mod and the need to bump the charging voltage up with the AGM to keep them healthy. My voltage booster should arrive any day now.
 

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2007 Forester Sports XT 4EAT
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While my FXT's battery is doing well at just over a year old, I've been considering a better one given past experience, and with winter on the doorstep.

I monitor my vehicle's voltage constantly... it's the display I have as primary on my radar detector. It is mostly at 14.3v, lowering to the 13s after enough running time, but always 14+ at startup.... which is the point of my post and your quote: how much voltage does an AGM battery require for its "higher charge voltage"??
Any AGM battery designed for a vehicle will work with the standard alternator output, but may not be optimal for the battery.

For the Optima Yellow top battery... other brands could differ, so refer the manufacturers battery specification:

• Open Circuit Voltage (Fully charged): 13.1 volts ◄ A conventional wet battery will measure 12.6 volts.
• Alternator Recommended Charging Voltage: 13.65 to 15.0 volts ◄ Installing the "alternator diode MOD" keeps the voltage in the 14 to 14.8 volt range.

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
 
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