Keep car alive on charger while replacing battery?

[bde]

I have seen advice elsewhere recommending connecting a battery charger/maintainer to the underhood jump-starting lugs before disconnecting the old battery so that nothing in the car freaks out due to loss of power.
I understand that doing so would mean that the battery terminals would be 'live' after they are removed from the old battery, so additional insulating/isolating precautions are required.
Is this a good or bad idea?
Thanks in advance!

 

[stefdds]

You can purchase a 9V battery adapter that plugs into the 12v lighter outlet if you wish to keep your settings "live" for the radio, time, seats, etc. in the memory of these units. Otherwise, disconnecting the vehicle battery won't cause any harm ; in fact it is often recommended in the oem manual when doing certain tasks/jobs. (and as far as I know, it is not stated anywhere to "back feed" current while the vehicles battery supply is disconnected.)

However, operating and running tasks, like Parking Brake for pad change etc , or running down the module(s) voltage from use during testing without supplemental power (battery charger) CAN cause potential damage .

See > Ross-Tech EPB YTube video. <

 

[Uwe]

You can purchase a 9V battery adapter that plugs into the 12v lighter outlet

That may not work as well as it used to. Many newer cars only supply switched power to the 12V lighter outlet, meaning it's essentially disconnected when the ignition is off, and a 9V battery isn't going to be able to supply enough current to run all the things that will be ON if you try to do this with ignition on.

Whether a charger/maintainer will do the trick depends on the logic in it. I'd suggest a constant-voltage (12-13.8V) supply rather that a "charger" or "maintainer", or use another battery, it can be a relatively small one, like one you'd find in a typical computer UPS.

-Uwe-

PS: Moved to General VW/Audi Repair.

 

[RGH0]

Modern "smart" chargers usually need to see the battery in order to supply power. The Ctek charger I use has a 12V power supply option to keep power to my Cars if needed when i remove the battery

 

[Uwe]

Modern "smart" chargers usually need to see the battery in order to supply power.

Yup. That's why I said it depends on the logic in it.

-Uwe-

 

[bde]

Whether a charger/maintainer will do the trick depends on the logic in it. I'd suggest a constant-voltage (12-13.8V) supply rather that a "charger" or "maintainer", or use another battery, it can be a relatively small one, like one you'd find in a typical computer UPS.

I have the perfect programmable industrial battery charger/power supply for this. Thank you for the input Uwe!
(and also for moving this thread to it's proper place in General VW/Audi Repair)