A neighbor called AAA to jump-start her car. He arrived with a new battery. He jump-started the car and, with the engine running, removed the old battery and installed the new one.

I recall from an Auto Shop course (1973) that the battery acts as a current stabilizer and you should never run the engine without one installed because of possible damage to the alternator. The YouTube videos don't mention this.

Some cars dump settings (radio, nav, etc.) when the battery is disconnected. Maybe that's why the AAA guy did what he did.

I've prevented the dump by connecting a 12V gel-cel to the battery cables prior to removing them from the battery. Not required on my 2017 Accord V6.

Comments ?

I’d be concerned about sticking my hand in the fan blades.

Unless he knew that this was possible with your specific car, I'd be worried. I tried this once and fried the instrument panel regulator.

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Release the Kraken

Do cars have fan blades anymore?

Just curious but would changing a battery on my diesel truck be a potential problem because I have two batteries? Are the two batteries connected in parallel so that one will still be providing power to the vehicle if the other is removed? I wouldn't think the two batteries would be independent of each other. I have been told the two batteries are required for turning the motor over for starting and to do that, they would have to be connected in parallel.

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Bill

Good friend in gun club has auto repair shop, he used the “ supplemental” 12VDC device when changing batteries in newer vehicles to prevent loosing settings in vehicle.

I would love to ask installer why he did that

I had a Yukon, I think a 2000, and I needed SAE and Metric sockets to change the battery. My 2008 SS Impala I had to remove a cross brace to get the old one out. After that, I've bought a couple since and the auto parts store does it for free.Those double-battery cars I think have some kind of electronic gizmos in there between the batteries some place that magically change from needing both to just one. I think.

I had a duel battery HD 3/4 ton 4X4 pick up truck. I did a lot of snowplowing and that would pull the battery/s down real good!

I talked with 4 well thought of mechanics and not one of them agreed how the system worked. ( I never did find out just what was what.) I will tell you that I found it best when hooking up a charger was to do one battery till the battery was up and them move the clamps and go to the other battery.

As far as changing a battery I had a 15 Corvette (C7), the battery was in the trunk and it was a super PITA to change. It was like the engineers(So Called) went out of their way to make a change as difficult as they could.

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14 S&W Revs none with locks!

In my personal experience, even when a battery is completely disconnected for a short amount of time, almost everything retains its memory (seats, adjustments, radio stations etc.) and the few things that are temporarily lost, do relearn themselves within a few mlles - such as the tire pressures, time on the clock (if you have GPS, On-Star or similar).

I changed the battery on my Wife's car a little while ago and didn't have to reset anything at all after droving a few miles. Granted, my Wife's car does have a lot of gadgets and do-dads, but I would think most cars theses days do as well.

IMHO I would NEVER change a battery while the engine was running!! In fact, there is little I'd ever do while the engine is running EXCEPT check the fluids like the Tranny and PS fluid which require the car be hot and running when checking. Just common sense to me.

A good friend has a older Ford diesel and one winter when he was in warm and sunny Florida, it went dead. I checked the owner's manual and it said to put the charger on the right hand battery when facing the front of the vehicle. Charging that battery, charged them both.

I don't know if any other 2 battery systems are the same or not. The manual may tell you.

If your car isn't equipped with a factory unit, you can buy a memory saver.

This tells me there's a diode (one way component) between the two batteries. My motor home was like this, designed to prevent the house battery from discharging the main battery, so you could always get started again.

The battery is there for weight distribution and handling. Pfft, who cares about maintenance.

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Release the Kraken

No, most vehicle's have electric cooling fans, not belt driven fan blades.

Point taken!

With that said its probably easier to break into Fort Knox than pull the battery in that car. I had other Vettes (Z06) with a trunk battery and it was easy. Course I have the hands of a gynecologist and reaching those big mitts down to the battery was giving me a nasty time.

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14 S&W Revs none with locks!

They're in parallel to provide more starting amperage and capacity without having to up the voltage.

I spotted this guy driving like this. I have no idea what was going on.

Attached Images

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I told you not to use Lifebuoy

I spotted this guy driving like this. I have no idea what was going on.
In regard to th OP’s question, it used to be a common way to test the alternator was to pull a battery terminal while a car was running. If the car stayed running, the alternator was putting out. How many amps though?
The practice is frowned on in later model cars. I’ve heard it could cause a voltage surge or blow a diode somewhere.

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I told you not to use Lifebuoy

I read (on the internet, of course) of another way to check the alternator. Start the engine and open the door, so that the interior light is on. Turn on the headlights and if the interior light dims, the alternator needs to be replaced.

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John 3:16
WAR EAGLE!

Did you happen to be in a county East of here when you saw that Mustang?! (I'm kidding, of course, but a lot of strange stories come from out that way.)

It depends on your alternator and regulator setup weather you can disconnect the battery while running. Some of the old internally regulated GM setups would cook the alternator if you did that. But. I see no advantage in doing it running. I see lots of reasons it is a bad idea. If he was worried about settings, memory etc., he could have just connected his jumper cables. Neg to any ground and positive on positive cable.

My 97 Ford Powerstroke has 2 batteries, manual states to jump with passenger side battery. I don't believe there is a diode in between it would be a dandy for that many amps when starting. I believe it is due to the fact the passenger side battery has shorter cables to both starter and alternator.

He was being trendy by converting his Mustang to an electric vehicle!

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Bill

No, that was right here in Allegheny County. McKeesport to be exact.
There is no shortage of weirdos here either.

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I told you not to use Lifebuoy

I’d be concerned and here’s why.
Just today a AAA tow driver came through our lot and made several passes. He eventually got out and asked about a vehicle he was supposed to pick up.
HE HAD THE KEY so we took it from him and hit the red button. The vehicle flashed and honked and it three cars away.
He either stated he didn’t think of doing that or he didn’t know he could do that.
We didn’t make him feel bad but oh my goodness.

Not belt driven but they have cooling fans. Sometimes two.