AGM vs. flooded lead acid batteries

[TJ Jim]

When I first bought my TJ six years ago the battery was weak so I replaced it with an AGM. So six years later it was time to get another one. Couldn’t find an AGM so I bought a cheaper lead acid battery. The AGM from new never charged much past 12.8v. This lead acid battery is charging and staying at 14v.

Just an interesting observation.

 

[macleanflood]

The TJ charging system was designed to charge lead acid batteries. The charge voltage is set for that battery chemistry. The temperature sensor (if equipment) is set to raise that charge voltage to assist lead acid batteries in the cold.

Couple of work arounds for running AGMs...add a 40k Ohm resistor in place of the temp sensor which gets charge voltage to 13.8 - still not enough but closer.

Run two batteries...lead acid and a second AGM with a DC to DC charger that's built to deliver the higher 14 to 14.8 charge voltage.

HP Tuners...use it to change the charge voltage range in the PCM.

And I suppose you could interrupt the PCM charge circuitry and replace it with an adjustable external regulator - but I dismiss this option as overly complicated and as expensive as the HP Tuners option.

And honestly these days if you can find a decent battery then run it, chemistry be damned.

-Mac

 

[JKP]

A fully charged flooded battery should be around 12.6 V at rest, an AGM 12.8 V.

If your flooded battery is 14 V at rest, somethings not right.

Also, O'Reilly has 20% off online orders and will ship an AGM to your doorstep for free.

 

[TJ Jim]

Seat of the pants it seems to run better with a lead acid battery. Doubt there’s Anything wrong with my charging system. Been running perfect and the same the six years I’ve owned it. Except for the water pump I had to put in couple of months ago.

 

[ColoJeep]

The TJ charging system was designed to charge lead acid batteries. The charge voltage is set for that battery chemistry. The temperature sensor (if equipment) is set to raise that charge voltage to assist lead acid batteries in the cold.

Couple of work arounds for running AGMs...add a 40k Ohm resistor in place of the temp sensor which gets charge voltage to 13.8 - still not enough but closer.

Run two batteries...lead acid and a second AGM with a DC to DC charger that's built to deliver the higher 14 to 14.8 charge voltage.

HP Tuners...use it to change the charge voltage range in the PCM.

And I suppose you could interrupt the PCM charge circuitry and replace it with an adjustable external regulator - but I dismiss this option as overly complicated and as expensive as the HP Tuners option.

And honestly these days if you can find a decent battery then run it, chemistry be damned.

-Mac

I get the theoretical discussion on charge rates for FLA vs. AGM , however it doesn't really seem to matter in the real world . Otherwise people would stop using AGM's . I put a AGM in my 99 in 2010 , the charging system is totally stock . The NAPA Legend , ( East Penn ) is still performing well today . Am I the only one that's dodged a huge problem ?

 

[macleanflood]

I regularly top off my AGM...weekly, overnight on a charger...

You're probably just fine if you get a decent AGM. But my theory is you're decreasing the lifespan.

Mine's also an Optima Yellow Top...deep cycle...I can run my fridge for two days after I top it off with a charger and I get 12 if I use the TJ charging system. That might be less AGM and more Optima. Sample size of 1.

Most folks don't spend the extra money for an AGM...unless the vehicle requires it...and if it requires it they're designed around that charge voltage.

-Mac

 

[ColoJeep]

I regularly top off my AGM...weekly, overnight on a charger...

You're probably just fine if you get a decent AGM. But my theory is you're decreasing the lifespan.

I guess I got decent AGM's . All 4 vehicles have them now with stock charging systems , (Two TJ's , a 98 4Runner and 04 Taco) , the newest was new in 2020 , the oldest in 2010 . That's much better life than I ever had with FLA batteries in the Rockies . Thanks

 

[L J]

I get the theoretical discussion on charge rates for FLA vs. AGM , however it doesn't really seem to matter in the real world .

yes - IMO it's more internet hype than practical reality

Am I the only one that's dodged a huge problem ?

no - I'm on my 3rd AGM (DieHard Platinums, Odyssey Extreme) in ~20 years with the OEM charging system

 

[g.hayduke]

I put an Odyssey AGM in my 06 and ran it for 8 years without any issues whatsoever. I replaced it with another Odyssey only because it was 8 years old. It still works perfectly after 8 years.

If my rig will be sitting for a couple weeks, I hook up my CTek charger with an AGM setting.

 

[tworley]

5 years with my Northstar AGM. Though since 2021 the jeep has not been a daily and the jeep sits in the garage with a maintainer on it

 

[Chris]

I wonder how those AGM batteries hold up in a place like Arizona where the heat just destroys batteries. Every lead acid battery I had in Arizona never made it past 2 years.

 

[TJ Jim]

My AGM lasted six years, and the biggest reason I replaced it was because the harbor freight toaster battery tester said it was weak. Supposed to be 750cca but was reading 400. It never let me down but after my 2020 ram died after a trip to town unexpectedly I wanted to get ahead of the game. It’s been reading 11.8v for months so I said screw it and replaced it.

 

[jwtj02]

I recently picked up a yellow top and, because it isn't a daily driver, followed @macleanflood 's advice and make sure to keep my NOCO charger (that has an AGM setting) on periodically.

 

[John Cooper]

I haven't checked with my scanner, but the dash gauge shows it's charging right at 14 volts on my AGM battery

 

[L J]

I haven't checked with my scanner, but the dash gauge shows it's charging right at 14 volts on my AGM battery

I believe our '06s have dummy oil/ water/volt gauges.

 

[John Cooper]

I believe our '06s have dummy oil/ water/volt gauges.

Probably do. I may check it with my scan tool....... at some point in time

 

[ColoJeep]

I believe our '06s have dummy oil/ water/volt gauges.

I know the oil pressure gauge is a idiot light wanna be , but temp and volt , I don't know if they're real on not.

 

[JKP]

Temp and Volt are "real", but the PCM damps the movement. If you want to see the temp, volts real-time, use a Bluetooth reader with your phone.

 

[John Cooper]

Temp and Volt are "real", but the PCM damps the movement. If you want to see the temp, volts real-time, use a Bluetooth reader with your phone.

Or hook up your Matco scanner

I might do it later today, but the stupid power steering line on my SIL Honda car honestly spanked my butt today.

 

[ColoJeep]

Temp and Volt are "real", but the PCM damps the movement. If you want to see the temp, volts real-time, use a Bluetooth reader with your phone.

Or have a vehicle with real gauges like , 02 and older , before our German friends " improved " the TJ .