Battery Gauge Dancing Around

I'm sure all of us once in a while get the "Battery Charging" message. Seems that for the past few days my battery gauge has been moving up and down between the tick to the left of center to the tick right of center. When I'm on the gas, its to the left of center. When I leave off, the needle move to the right of center for about 5 seconds, then moves back. If I'm still coasting after that, a few seconds later its back to the tick right of center. When I go back on the gas, it moves back to the tick left of center, and so on...

Battery? Alternator?? I need to make an appointment I guess. I think something is about to die.

Joe

 

I'd check your connections on your alternator and if "good" I would default your assumptions to needing a new battery...

 

There was another thread about this where the consensus was that’s it’s normal for the 22s. My 18 moves up when giving it gas and back down when RPMs drop like when I’m coasting or idling.

But since you’re under warranty, you could get it checked out so it’s documented if something fails later. Just make sure they don’t charge you a diagnostic fee.

 

That's a good idea. Once its documented I would at least have some leverage.

 

Thats modern electronics at work. Apparently that's how modern vehicles charge the batteries now, it's on demand rather than a constant 13 volts. My wife's Ridgeline's voltmeter is rock solid when it's running but when you plug in a voltmeter to the charging port or even the battery you will see it's actually pulse charging the battery as well. If you do a search on here, a guy has a full spreadsheet that dives deep into this.

 

That’s normal, the alternator charges the battery on deceleration because it doesn’t use any fuel and it stops charging the battery on acceleration or cruising to improve fuel economy. This will depend on the state of charge of the battery though. If the charge in the battery is too low, the alternator will keep a steady voltage on it. The left tick mark is around 12V and the center is around 14V.

 

This is all normal. If it never fluctuated (or was in the bottom or top 25% when it shouldn’t be), I’d be more concerned. If it seems drastic, I’d blame that on hyper-accuracy with data on demand and a “zoomed in graph” if you will, if anything. The alternator is not constantly generating, your battery is under constantly variable loads, and your oil pump is going to work harder as you gas it so you’ll see pressure increase every time you increase in RPM

 

They fill these trucks with very thin oil. They do this for MPG. These trucks will idle with very low oil pressure and it will go up when on the throttle.

 

I have learned all of the above seems true. I had them look at it this morning. Battery is fine, and the alternator is putting out what it should. I've had the truck since April and have never seen the battery gauge jump around like that but I guess that's how it all works

 

100% normal. It’s for fuel mileage. Most new cars do this. No charge on acceleration. Full charge on braking. Just remember when you replace a battery it needs to be programmed or the truck will fri the new battery thinking it’s old.

 

what needs to be programmed? How would it fry it? Wouldn't the computer just measure the voltage in the battery and act accordingly?

 

So the module on the negative battery terminal monitors amps in and out(it’s a shunt). New cars and our truck use a flooded or agm battery which shouldn’t be charged at a steady voltage. They need high charge then low charge. When you accelerate the alternator drops for fuel and power then when you brake they load up for engine braking/regen if you want to call it that. When battery’s age the charging profile changes. If you just put a new battery in without telling the ecu it could overcharge or damage the battery with its charge profile. There are good YouTube videos about this with bmws killing batteries within a year or so. I’m vw Land we have to have speical 12 volt chargers/maintainers that vary load for these battery’s. These chargers are not cheap also. It’s all in telling the ecm it has a new battery to modify the algorithm. We scan the batteries bar codes and serial numbers to let the ecm know it’s been changed in vw I assume Toyota is similar. I can ask one of the toyota tech at my dealer tomorrow if it’s the same if you want.