H3 Want to upgrade my battery

[bigwilliedw01]

This one will fit the stock cover.

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[RamRod]

You're kidding, right? You know that isn't a car battery.

What about it makes it not work for a battery in a car? It's been going great for a month now and I have had zero issues with it


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[rascole]

What about it makes it not work for a battery in a car? It's been going great for a month now and I have had zero issues with it


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That is designed for a UPS system, not a car. It is engineered to sit still on a shelf and not bounced around in a Hummer. Made for slow trickle charges and not high amp discharges from an alternator. Internals will fail. Just because it fits doesn't make it right. Would hate to see your Hummer short out and catch on fire.

 

[RamRod]

The battery shop I bought it from said that it came from an AT&T tower? And other than its difference in original use I t's an AGM battery that would work where ever you can fit it in a 12 volt system.

Not that I am second guessing you or anything, what's a UPS system?

Interesting comment on the charging as well: http://lit.powerware.com/ll_download.asp?file=BAT04FXA_Oct08.pdf

So the above link says it made for 50 amp charge... Which is lower then what the alternator puts out by a significant margin.....

I will do some more digging to see if it needs to go, but so far it has been amazing to have while running he fridge/freezer!


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[rascole]

Uninterruptible Power Supply. Used for critical systems that cannot lose power in the event of a power failure. Mainly used for large computer systems like I have here in an oil refinery. Power goes out, the batteries take over. Most of these types of batteries have a low temp rating too. They are not designed for a hot engine compartment, our systems give an alarm at 110 deg.

 

[RamRod]

Thanks for the good info, make sense why they came from AT&T now! Must have been for one of their systems

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[JPaul]

Since it's AGM the vibration shouldn't be an issue, plus those batteries are true deep cycles so the plates are going to be thicker. Since it's so large the discharge current for the starter isn't going to be much of an issue either, though it might shorten its life, I'm not really sure. The specs list a limit of 800 amps for 5 seconds, pretty sure our starters don't pull anywhere near that much.

As for the charging, it is possible that the alternator might try to put too many amps in, but I don't think it will be by a lot. A 140 amp alternator isn't going to generate that many amps at idle and even most cruising speeds, plus a good chunk of it goes to running the engine and body electronics. You won't really know until either measuring the charging amps going in using a high capacity ammeter or find someone that knows how the charging controls are programmed. Honestly I'd be more concerned about undercharging rather than over charging.

 

[amrg]

Add to that when the engine bay is Hot a 140 amp alternator will give a max of 110-120 amps at full power

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[RamRod]

Man so much good info here!! Keep it coming

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[4speedfunk]

Jeep Grand Cherokees use a temp sensor in the tray under the battery. The sensor sends a signal to the puter which reduces the alternator output according to case temperature. Without the sensor, the alternator can overcharge (and overheat) the battery, so Jeep came up with this variable output system.

For this reason dead batteries and dead alternators are often misdiagnosed on ZJs & WJs. It's a "fail open" sensor and when they go bad...the puter sees a high temp reading and cuts the alternator output to near nothing. So you can replace both the battery and the alternator repeatedly and it will only be temporary. The real problem is often this tiny hidden sensor. It is very inconspicuous and many mechanics don't even know it's there. It's a tiny spring loaded button on the bottom of the tray, and it's wiring is entirely hidden below it.

I know guys that clip the sensor wires and connect them (to bypass the sensor). This forces the alternator to its max output which isn't good. I also know one guy that put a piece of 2"x8" under his battery because it was not the right size, and he had constant charging problems due to the insulating properties of the wood. THAT guy is the whole reason I found out about this sensor, and Jeep's variable charging system.

Moral of the story...battery size and type matter more than what it did in the 70s. I can see where a cool-running AGM battery might not work too well in a Cherokee for instance. Although the Hummer has no such temp sensor...we all know how finicky it can be about electrical things. It's probably monitoring the battery state, and varying the alternator output in other ways we might not understand.


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[CaseyS]

Pulling my knowledge from my swap, the Hummer has a variable field voltage output to the alternator coming from either the ecm or bcm. I could not get this to work properly with my swap since the ecu probably did not know very well what was going on. I ended up wiring my cs144 alternator in a typical "3wire" configuration with a charge wire to the battery, a turn on wire to switched hot, and the voltage sense wire I think that I routed to the main fuse on the distribution block.

So Hummer does have a variable voltage charging system, just not sure what the inputs are and what parameters control the alternator field.

 

[4speedfunk]

Yeah...I figured as much. It's probably more high tech than simply sensing the battery temperature.


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[bigwilliedw01]

This is my current setup with dual Optimas, Red Top primary and Yellow Top aux. Genesis Off-road dual battery box with 200 amp auto isolator. Will fit any group 34 size batteries.

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