I had to do a jump start the other day. 6 weeks idle while I was OS working (Chile).
Tried to jump it from a charged (slightly smaller) spare I had, but ended up having to swap batteries.
I guess too many cable losses and inertia to get it over the line.

Once running - I would have liked to then simply swap batteries back, but was concerned I might do some damage to the smarts.
If I could swap - that way I could have driven her around for a while to recharge it.
In the end I took the dead battery home and put it on the charger for 24hrs - (not preferred)

Anyone successfully swapped batteries - (like the good 'ol days) - with the car running - or is it now a thing of the past?

 

thing of the past.....too many electronics.....

 

Even in the past, that was a bad idea, just not as sensitive as today's electronics. When ever possible, you should always bring a battery back to life using a battery charger. An alternator is designed to maintain battery voltage. Charging a battery from dead using an alternator requires a huge amount of amperage. Large draws like that can greatly reduce the life of the components in an alternator. Yes I know it is done all the time, but that does not mean it is the best way to handle the issue.

James

 

In the old days we might install a new battery that way, but never to charge a dead one. James is certainly right. A lot of load for the alternator to handle, and that battery may well have a dead cell in it. That could be why it is dead, or worse yet a damaged cell, that will short. Now, you have a dead battery and a dead alternator....

 

Gosh, I don't know from experience with newer cars. I know for a fact it was safe on a 60's car. Heck, I did it! I would hope the alternator would supply enough Umph at idle on newer than 60's cars that it could be done ..... safely. If you so it, let us know.

Les

 

Needs juice to fire..... Low voltage and you have rough running car, no voltage, no run.....lol

 

thanks guys - thought as much...
but I would have suspected the car's regulator circuit would have controlled the Amps....well maybe not in a 60's truck...;>)

 

Used to be able to do it in the old days with a 37A alternator and dumb electrics but back in the early 70's I did some tests for the SCCA relating to kill switches and saw spikes over 200 volts if you disconnected a battery while charging.


Reason is simple: ELI the ICE man. A battery is like a big capacitor. Disconnect the battery while at a high charge and suddenly the amps go to zero and while the field is collapsing, the voltage goes through the roof.


Modern 100A+ alternators and fragile electrics just make this worse.


So before swapping batteries, shut the engine off.


Note: you can generally disconnect jumpers with the engines running because each still has a battery in the circut.