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[zuke]

I haven't stayed at any hotels recently, but I am an aircraft mechanic. None of your readings seem extreme, and since the system is digitally controlled it isn't unusual to get large variations in how it chooses to charge the battery (especially with an AGM). It's possible that the battery is marginal, hence the low 12.1V when cold, but otherwise it seems like everything is working as it should and is generally up to the task.

I've been thinking for a while that for some reason the BMS likes to run the system at a slight deficit rather than fully charge the battery. Your observations seem to be in line with this, and others have noted it as well. I'm not that familiar with AGMs, but perhaps this is meant to protect the battery in some way.

Edited to note: 12.1V was a different member.

The other member is experiencing very similar behavior, So it's probably relevant to both of us..

My battery is at 12.2 this morning, which is the lowest I've seen it in the morning, while it was at 12.6 when I parked it last night. It really is looking like a marginal battery. As you noted, all the number seem to point to everything else functioning fine.

I've seen several members have been keeping their Broncos on maintainer/trickle chargers at night, but that's not really an option at my house, and I think just hiding the problem.

Gonna run what battery tests I can today, and see what I get, If I can't get a conclusive answer doing that, I'll take to one of the stores with an actual Carbon Pile tester, and see what that says, if it doesn't come up 100%, I'll replace it. Gotta research batteries to, I've been using Duracell/East Penn's in my jeeps, but I'm not sure that's the best choice for the Bronco...

Anyone got inputs on Batteries?

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[zuke]

Checked voltage at battery this morning 29° outside
At battery 12.1 volts not running
Running at battery is 15 volts
Dash reading 15.3
No warning lights

35 Degrees here, 12.2 before starting, Start up and goes to 14.6 on the dash, 14.8 at the battery. By the time it's at a low idle the guage is down to 13.4 and the battery was reading 12.8... shut it off and the battery almost immediately dropped back to 12.2.

So slightly different behavior than yours, but maybe that's the difference between 12.1 and 12.2. From what I'm reading that is actually a pretty big difference with an AGM (Like 75% charge vs 60% charge)

 

[LockedBronco]

35 Degrees here, 12.2 before starting, Start up and goes to 14.6 on the dash, 14.8 at the battery. By the time it's at a low idle the guage is down to 13.4 and the battery was reading 12.8... shut it off and the battery almost immediately dropped back to 12.2.

So slightly different behavior than yours, but maybe that's the difference between 12.1 and 12.2. From what I'm reading that is actually a pretty big difference with an AGM (Like 75% charge vs 60% charge)

That is what I am finding out. Looks like AMG is only battery that can be used.

 

[zuke]

That is what I am finding out. Looks like AMG is only battery that can be used.

Yeah, It calls for a Group 94R AGM with 800CCA

Interesting drive from the house to the shop, 10 Miles on surface streets with a fair number of turns and lights, Each time I'd slow down for a turn it would briefly get into the upper 14's for a few seconds before returning to the mid 13's again, there is a long light right before I get to the shop (about 5 minutes) and while sitting at the light with A.S.S. disabled it would go about 10 seconds at 13.2~13.5 then drop to 12.5 for an equal amount of time, it repeated that the entire time I sat at the light...

On arrival at the shop, the dash was showing 13.2, and the battery was at 12.7, turned it off and the battery dropped to 12.4.

I think the battery may be driving the PCM and regulator crazy....

Looking at the rear of my JKU which is making funny noises (Suspect a bad rear drive shaft) Then I'll get back on the Bronco battery a bit later.. (Gotta have the JKU ready for DD Duty in case I have to take the Bronco off the road for a bit!)

 

[LockedBronco]

Yeah, It calls for a Group 94R AGM with 800CCA

Interesting drive from the house to the shop, 10 Miles on surface streets with a fair number of turns and lights, Each time I'd slow down for a turn it would briefly get into the upper 14's for a few seconds before returning to the mid 13's again, there is a long light right before I get to the shop (about 5 minutes) and while sitting at the light with A.S.S. disabled it would go about 10 seconds at 13.2~13.5 then drop to 12.5 for an equal amount of time, it repeated that the entire time I sat at the light...

On arrival at the shop, the dash was showing 13.2, and the battery was at 12.7, turned it off and the battery dropped to 12.4.

I think the battery may be driving the PCM and regulator crazy....

Looking at the rear of my JKU which is making funny noises (Suspect a bad rear drive shaft) Then I'll get back on the Bronco battery a bit later.. (Gotta have the JKU ready for DD Duty in case I have to take the Bronco off the road for a bit!)

Wow that is exactly what mine was doing. Now is 14.9 - 15.3 all the time.

My back up is a 72 that gets 5 miles to the gallon

 

[zuke]

Wow that is exactly what mine was doing. Now is 14.9 - 15.3 all the time.

I'm thinking all my shenanigans yesterday put more of a charge on the battery, and now I'm back to where we were before our batteries got low enough to call for the higher charge rates, I wouldn't even have noticed this kind of pattern before I started actually seeing the crazy high charge rates and watching things so close.

Checked out the Duracell, and Batteries plus doesn't even recognize a Bronco, so couldn't get a definitive "right" battery listing on it, But this looks like it's probably it;

https://www.batteriesplus.com/product-details/auto_light-truck/battery/duracell-ultra/sli94ragm

My back up is a 72 that gets 5 miles to the gallon

Ouch!

Not the driveshaft on the JKU, but I'm having trouble getting it to even reproduce the noise on jackstands, It's got 91,000 miles on it, which is usually where the rzeppa joints normally give up but they look fine.

 

[LockedBronco]

I'm thinking all my shenanigans yesterday put more of a charge on the battery, and now I'm back to where we were before our batteries got low enough to call for the higher charge rates, I wouldn't even have noticed this kind of pattern before I started actually seeing the crazy high charge rates and watching things so close.

Checked out the Duracell, and Batteries plus doesn't even recognize a Bronco, so couldn't get a definitive "right" battery listing on it, But this looks like it's probably it;

https://www.batteriesplus.com/product-details/auto_light-truck/battery/duracell-ultra/sli94ragm



Ouch!

Not the driveshaft on the JKU, but I'm having trouble getting it to even reproduce the noise on jackstands, It's got 91,000 miles on it, which is usually where the rzeppa joints normally give up but they look fine.

Lol Copper Top first time seeing them.

Did you pull diff cover?

 

[zuke]

Lol Copper Top first time seeing them.

I've become a fan of East Penn Manufacturing (The Maker of the Duracell) since Johnson Controls bought Optima and moved the manufacturing of those to Mexico. Quality went to crap.

East Penn is one of the few battery makers left that Johnson hasn't purchased yet...

Did you pull diff cover?

I'm thinking I won't have to, Pulled the wheels and found the noise, it looks like a slightly warped rotor, Got all the parts and doing the rear brakes right now.

While I was at Oreilly's I had them throw the tester on the Bronco, It said everything checks out and the battery just needs a charge.. That could go with @KABQ 's suspicion that the BMS doesn't keep the battery fully charged.

 

[KABQ]

Just to add a data point I checked my battery across the terminals a few minutes ago. The vehicle had been sitting for roughly 17 hours after 3 short trips yesterday (about 5 minutes each). At 39° it read 12.06V. No difficulty starting and everything worked normally. Dash read 15.2V for the entire 10 minute trip.

 

[zuke]

Just to add a data point I checked my battery across the terminals a few minutes ago. The vehicle had been sitting for roughly 17 hours after 3 short trips yesterday (about 5 minutes each). At 39° it read 12.06V. No difficulty starting and everything worked normally. Dash read 15.2V for the entire 10 minute trip.

Interesting data point.

I wonder if the charge program is changeable in the PCM to make it a bit more aggressive..

 

[zuke]

JKU is still making the noise after the brake job.... Gonna have to have some one else listen to it from outside while I drive it to pinpoint it... Sounds external to the axle, and more like a squeak or a chirp than a grind.. I can't figure out where it's coming from sitting in the driver's seat.

Moving back to the Bronco, pulled it into the shop, and the battery is sitting at 12.26, gonna run a few tests, than put a charge on the battery and see how it behaves for the next few days. If the charging system is just gonna run it down again, I don't really want to go buy a new battery yet...

 

[zuke]

Well the my Innova OBD Scanner said everything's great , the alternator is good, and the battery is fully charged at 12.22, (Down from the 12.26 when I pulled in...) Plugged in my automatic charger and it went to 30 amps...

 

[LockedBronco]

Backing plate?

Wouldn't battery be under warranty?

 

[LockedBronco]

Well the my Innova OBD Scanner said everything's great , the alternator is good, and the battery is fully charged at 12.22, (Down from the 12.26 when I pulled in...) Plugged in my automatic charger and it went to 30 amps...

Interesting

 

[zuke]

Backing plate?

It sounds a LOT like a backing plate... Checked those first

Wouldn't battery be under warranty?

Should be, But I'd rather poke my eye out than leave it with a dealer for 3 days to diagnose it, and say it's fine... Plus when they see the terrible things I've done to the electrical system on this thing they'd probably deny me anyway (And they might be justified!) I've swapped out the headlight switch, for one with fogs and wired those in, Put the amps in, and several other things I've played with...

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