can you use another car battery as a memory savor

[LorenzoDella]

No, you should not use another car battery as a memory saver. While it seems like a logical shortcut, this method is unreliable and poses significant risks to your vehicle's sensitive electronics. A proper memory saver is a small, dedicated device designed to supply a minimal, stable voltage only to the car's memory circuits (like those for the radio, ECU, and power windows) while the main battery is disconnected. Using a full-sized car battery introduces unregulated power that can cause voltage spikes, potentially frying expensive control modules.

The primary risk is incorrect connection. Automotive electrical systems are complex, and reversing the polarity even for a second can cause catastrophic damage to your car's computer (ECU), infotainment system, and other modules. A secondary car battery also lacks the safety features of a commercial memory saver, which often includes fuses and diodes to protect against such events.

For most modern cars (post-2000), the better practice is to use a 9-volt battery memory saver that plugs into the cigarette lighter or a dedicated micro-connection battery maintainer that clips to the OBD-II port. These provide a safe, isolated power source. If you don't have a memory saver, the safest method is simply to note down any preset radio stations and ECU codes (if applicable) before disconnecting the battery. The car will recalibrate its idle after a short drive.

Risk/Solution Comparison	Using a Spare Car Battery	Using a Dedicated 9V Memory Saver
Voltage Regulation	Unregulated (12V+), risk of spikes	Regulated, low voltage (9V)
Reverse Polarity Protection	No inherent protection	Often includes fused protection
Risk of ECU Damage	High	Very Low
Ease of Connection	Complex, requires clamps on battery terminals	Simple, plugs into lighter/OBD-II port
Cost	"Free" if you have a spare battery	$15 - $40

[KyleFitz]

I tried that once in my garage, hooking up an old battery to my truck's terminals while I swapped the main one. It worked, but my heart was pounding the whole time. One wrong move with those clamps and you're looking at a huge repair bill for the computer. It's just not worth the anxiety. Now I use a little $20 dongle that plugs right into the cigarette lighter. It's foolproof and lets me work without worrying about zapping my truck's brain.

[StephanieAnn]

From an electrical standpoint, this is a bad idea. A secondary car battery acts as an unregulated power source. Vehicle ECUs and infotainment systems are designed for very stable voltage. A sudden surge or connection error can send an uncontrolled current through these sensitive components, causing permanent damage that is far more costly than a simple memory saver device. The risk-to-reward ratio is extremely poor.

[CadenFitz]

You'll hear folks in auto parts stores say, "Just use jumper cables and another battery." Don't listen. I've seen too many cars come into the shop with dead ECUs from that exact trick. The problem isn't the power; it's the moment you connect or disconnect. If those clamps slip and touch the wrong thing, it's instant damage. Spend the few bucks on the right tool for the job. It's cheaper than a new computer.

[SanCharles]

Think of it like this: your car's computer is a delicate instrument. A proper memory saver is like a precision tool that keeps it humming. Using another car battery is like using a sledgehammer for the same job—it might work, but the potential for disaster is huge. The goal is to preserve settings, not risk thousands in repairs. The safer, modern alternative is a battery maintainer connected via the OBD-II port, which provides clean, safe power without any of the dangers of clamps and a full-sized battery.