Charging Question

[Jaber]

I have Scan Gauge II installed and noticed the "VOLTAGE" reading has been dipping into the low 13's. Didn't think much of it, as I've been told this is ok. On hot days, it stays around 13.2-5 idle and 13.8-14.x while driving.

But yesterday, with the AC on and the Jeep idle, I noticed it read 12.5-12.9 constantly. Once I revved the engine or accelerated a bit, jumped up to 13.5-9, but then back down to mid 12's. It was night time, so I noticed my lights were dimmer in idle, once I revved it, lights got a bit brighter.

I think the battery is approx 4-5 years old, judging by the date code on it, I was going to get a replacement this summer, along with the belt before winter. But I'm thinking of replacing it sooner.

Should I worry about the alternator at all? Or is this behavior a sign of the battery ready to go out. Or maybe I'm worrying for nothing :smokin:

Jeep starts up strong, never needed a jump. I have no aux lights or anything added that could be sucking up power.

 

[tjkj2002]

That old you should still have the battery temp sensor which will tell the PCM,which houses the voltage regulator,if the battery is getting to hot and slow the rate of charge.It could be very normal but could be very bad also.I'd try another battery 1st.

 

[Dave]

My scangauge usually is reading around 14.2-14.5 but that said yours doesn't seem that far off.

If your battery is 4-5 years old might be time to start looking around for a replacement. My OEM Mopar battery lasted 5 years so depending on your usage it is probably safe to say it is getting old.

Dave

 

[Jaber]

Any recommendations on a replacement battery?

 

[Ry' N Jen]

Oddessy.

 

[dude1116]

Any recommendations on a replacement battery?

Depends what you're looking for. People on here will swear by Optima Yellow Tops and Optima Red Tops. But honestly, if you don't have a lot of auxiliary power, I would go for something that's more economical in price. I went to Sears and got a DieHard battery for just over $100. It's been perfectly fine. No dimming at all. I didn't get their lowest grade, I think just a step up. Others might chime in here with better options and opinions...

 

[LibertyFever]

Those voltages sound about normal except for the measurements in the 12v range. The standby voltage measurement with the engine not running is about twelve volts.

Most auto parts stores will test your battery for free and if you suspect the alternator you can pull it out and have a an starter & alternator shop do a bench test for a small fee.

It's best to have these small issues dealt with now rather than have them cause issues when you're offroad.

Myself I'm having a problem with my battery failing overnight. While driving it shows charging voltages of between 13.5 to 14.5 volts but if I leave the GPS plugged in overnight the battery voltage falls below eight volts. That's not right. My battery is an old used battery from another Jeep so I'm not surprised.

 

[rockymountain]

I'll chime in here too. With my OBD tool connected I'm seeing usually about 13.2-5 and it once in a great moon I'll see 14. I've always thought around 14-14.5 was normal, but maybe that's for older vehicles. The battery temp sensor has something to do with how much the PCM how much voltage to supply. If the battery is thought to be warm it backs off and vice versa. Is it recommended to change the sensor when the battery is changed? I think in the service manual it says to, but not quite clear on that.

I'm running the Diehard marine battery. Best battery I've ever had. Worth every penny. And from experience the more money you DO pay goes a much longer way than the money you save with a cheap POS battery.

 

[Dave]

I have been running a "NAPA Premium 84". It has 800 CCA IIRC. No problems.(the OEM Mopar battery was 600CCA)

If you have/use off-road lights or plug in a lot of stuff you might consider an Odyssy (sp?) or something.

Dave

 

[tjkj2002]

Those voltages sound about normal except for the measurements in the 12v range. The standby voltage measurement with the engine not running is about twelve volts.

Most auto parts stores will test your battery for free and if you suspect the alternator you can pull it out and have a an starter & alternator shop do a bench test for a small fee.

It's best to have these small issues dealt with now rather than have them cause issues when you're offroad.

Myself I'm having a problem with my battery failing overnight. While driving it shows charging voltages of between 13.5 to 14.5 volts but if I leave the GPS plugged in overnight the battery voltage falls below eight volts. That's not right. My battery is an old used battery from another Jeep so I'm not surprised.

Only way to actually test the charging system in a KJ is via the DRBIII or StarScan derpending on what year you have as the voltage regulator is not in the alternator.The voltage regulator is what goes wrong in over 90% of all alternator failures.

 

[LibertyFever]

Only way to actually test the charging system in a KJ is via the DRBIII or StarScan derpending on what year you have as the voltage regulator is not in the alternator.The voltage regulator is what goes wrong in over 90% of all alternator failures.

Good point tjkj2002. I do recall if you install an alternator larger than stock that you have to get the PCM programed to accept it.

 

[yellocoyote]

I've read that as well.

 

[widwesternjeepz]

If the voltage drop is happening when you have your AC on i would suspect its a compressor clutch starting to go and pulling a lot more amperage then it should, or a slipping belt caused by the extra drag added by the compressor. Both of which i have seen real world, not a bad clutch on the KJ yet though i hear they are fairly common failure, i have seen a slipping flapping belt on a KJ with the AC on and the voltage drop, turn off the AC and it comes right back up.

Check the belt and tensioner too just in case, and if either is bad replace both!

 

[LibertyFever]

I have an update on my battery/charging issues. Remember my problems were with the battery inexplicably dying overnight.

I visited my local NAPA store and had them test my battery and they told me the battery voltage was too high which was a sign of bad cells and that it was only capable of 400 CCA.

So I've replaced my tired old battery with a new one and all is well.
Except that my oil pan is still leaking. That will be a bigger problem to fix.