Disconnect the battery

The Alpine stereo in the Polo 6N1 immediately loses its settings as soon as the battery is disconnected.

What methods do you use to maintain the battery voltage in such cases? I didn't want to purchase a charger like a CTEK MXS 7.0 or even an MXS 10.0. Unfortunately, my MXS 5.0 doesn't have this feature.

Hello!

I have this small, portable device, about the size of a women's handbag, that I kept from my previous self-employment.

Inside, there's a battery similar to the ones found in small motorcycles, along with some extras like a battery level indicator, a few indicator lights, and a switch.
The power then comes out through a cable, which is plugged into the OBD socket.

Replacing the battery once is perfectly fine.
Although it can also be done more cheaply using homemade solutions and a different battery.

However, when performing more extensive operations on modern cars, and when onboard voltage is also required,
Right now, the only thing that comes to mind is working on the electric parking brake.
That's obviously not enough.
Typically, the devices you mentioned are used in those situations.

I have one of those too.
"But I only use it as a charger myself."
That's already outstanding as a charger.
I just have to say this.

I always perform battery replacements without interruption using a 6A wireless power supply. You have to be careful about where you connect to supply power to the vehicle. My last "victim" for this method was a 2008 Touareg. In that case, I connected to the jump-start terminals in the engine compartment. The battery is located underneath the driver's seat that needs to be removed.

For some of your vehicles with a permanently powered cigarette lighter socket, this is also a viable option.

I prepared two 2.5mm² wires, each approximately 3 meters long. One end of each wire has a ring terminal, and the other end has an alligator clip. This allowed me to connect an old auxiliary battery to the terminals using the terminal bolts and remove the vehicle's battery.

It works perfectly.