jonesea74

Have a 97 Grand Cherokee...4.0 L

It seems to need a new battery every year. Took in the last one to have load tested and you could hear it boiling. Parts store said the battery has been over charging.

Replaced battery, connected DMM, voltage good. Started and voltage came up to 13.5 as expected.

Drove to the parts store had them check the charging system...said it was good...hmmm...so why it is going through batteries every year.

DMM is connected inside to watch voltage...never goes past 13.7 vDC.

Parts store recommends replacing alternator. Easy but I don't like replacing parts unless I know it is faulty.

Battery cables and terminals clean.

What to check? Voltage drop across battery cables? Maybe if was NOT charging. Poor ground? Voltage drop test would indicate a poor ground.

Any thoughts?

Thanks

dave1123

Welcome to CF!

Most people are not aware there is a temperature sensor underneath the battery that tells the PCM to cut back the charging rate when the battery gets hot. It looks like a round spring-loaded button in the center of the battery tray and can get corroded very easily if the battery boils over or leaks. I would guess yours doesn't work anymore.

rockauto.com has them for $18.

Bugout4x4

Sounds like it could be an amperage issue rather than a voltage issue. I have had Alternators that put out the proper voltage but were putting out far too many amps after the battery was fully charged. An alternator is designed to back off of amperage output when it is not needed anymore because the battery is full and demand is minimal, headlights off and Etc. Sounds like yours is not backing off amps like it should even though the voltage is correct.


The only other cause for this would be a possible intermittent direct high amp short while driving it, like the main cable that goes to the starter or distribution box. This would then cause the alternator to try and keep up with the high amperage draw and all these amps have to pass through the battery on their way to the short causing it to get cooked.

SteveMongr

Bingo!

Bugout4x4

This is good information to know Dave! Except I'm not sure his 97 has this sensor? My 97 does not have this sensor and relies on the alternator to be self regulating. This sounds like it would be a very good secondary safety device though!

Bustedback

How many CCA is your battery rated for?

dave1123

Who do you think you're messing with here? I checked rockauto before I posted that just to check if his jeep used one. LOL!

Another place where good poster info is necessary! After all, you own an XJ, not a ZJ.

Bugout4x4

Like I said, I was not sure about his Here's my thought though. This has got to be just a safety device, For engineers to override normal self-regulating alternator functions in exchange for a system under the battery reading temperature to control the alternator charging output would be absolutely ignorant. I truly hope it hasn't come to this level of engineering idiocy has it?

SteveMongr

Don't mean to go too far off topic but here goes.
I also have concerns about the function of sensor in battery tray. It does make more sense that it would be a secondary device, not to regulate charge current but to shut off charge if battery exceeds a specified temperature. A temp sender regulating charge current seems impossible or ignorant.

My concern regards this, I use a Viar 400 air compressor and Yellow Top battery to fill all four tires without engine running. This could cause battery to warm/heat up. Then when I start engine and cruise down the road, the battery may not be recharged at all if it became too warm. And I would be home and shut off engine before battery cooled down. This is just speculation, I have done no testing and have had no issues filling tires this way for three years, once or twice a week.

Bugout4x4

Yes...I think even the outside Ambient Temperatures might greatly affect the variables in a system like this?

dave1123

I'm in no way a computer guru nor an electrical genius, I'm just repeating Chrysler rhetoric. I, myself, wasn't aware if it until I had an emergency battery replacement at Battery World while on the road with my 00 WJ. The tech showed it to me and explained what it was. Then I checked on-line with Mopar about how it worked.

Bugout4x4

It's not you Dave, I do not doubt this is what you found. I am just having trouble understanding why engineers would even conceive something like that in the first place. But...know what? I am being surprised everyday, like a Stop Light Switch affecting how the Trans operates or a recall on wiper blades because of Static Electricity. They are just starting to get a little out of hand with over engineering some of these things Dave.

SteveMongr

Apparently the battery temp sender is used on a number of vehicles.
Here is what Dodge says;

Bugout4x4

Thank you Steve, I find this just incredible! Honestly, there is absolutely no need for this complicated engineering mess at all. They are just adding more things to break on purpose with this.


Well, once again I am blown away by the ignorance of "modern engineering" and have to stand corrected. Looks like Dave may be absolutely correct about this even though I still just can't fathom why they would even engineer something like this, but they did.


Sorry Dave...It was just so hard to believe they could actually mess up things this bad man. Like I say, the over engineering is just getting far too out of hand for sure.


Next Question I would have is "Can it be bypassed?" lol

SteveMongr

Bypassing may involve extensive modification, like placing a piece of insulative foam over sensor, lol. I have heard of folks finding a rag under battery.
Have also heard of removing the sensor and installing a resistor in its place. The resistor would need to be correct.
Or perhaps remove sensor from tray and secure elsewhere.
I will leave mine as is.