Questions about a 9v Battery memory saver that plugs into socket

How many hours can you expect one to work?

The computer memory must be on the same circuit as the accessory or cig lighter circuit, if you blow that fuse, could you lose the memory?

What else is on the computer memory circuit?

I had a faulty one, it lost connectivity while replacing a thermostat. I thought something had drained the 9v battery, but that was not the case. The memory saver had an intermittent connection I later figured out, as the light indicating it was working would come and go by wiggling the wires. Luckily no problems resulted from loss of memory. In the Trailblazer you have to remove the alternator to get to the thermostat, thus directions were to disconnect the negative on the battery.

“How many hours can you expect one to work?”

That depends on how much power is being drawn from it (how many devices).

There is no harm done by letting the computer reset. This device is really made just to save your radio presets.

Those DC power outlets are pretty iffy. If you bump the device, it could easily become disconnected.

A fresh 9V battery has ~300 milliamp-hours of capacity.
A resting car needs no more than ~50 milliamps of current once all the electronics have gone to ‘sleep’.
So about 6 hours, except if electronics haven’t gone asleep or interior lights etc. come on when doors are opened.

The computer doesn’t have to be on the same circuit as the cig lighter.
Everything that gets 12V with the car off will ‘see’ the 9V battery.

Circuitsmith, my first thought was I killed the battery because I had the tailgate open and the lights drained the battery. But that did not seem to happen, although I don’t know for sure as the connector puked. Would the 9v try and power the lights? it did not seem so.

How did you hook it up? Some cigarette lighters are ‘off’ when the ignition is ‘off’, so one that plugged in there wouldn’t work.

I checked, my socket is active when the ignition is off. I had left my home made ac to 12vdc adapter for a cig lighter socket that plugs into obd at work, and for six bucks figured what the heck. Easier than going to work and I was at the parts store already. The number of circuits that are live, such as the 9v battery in an accessory plug saving computer memory is a curiosity to me.

It depends on how many modules/computers need to be kept alive with a 9 volt plug-in-cigarette lighter memory saver. Usually about 30 minutes max. Enough time to replace a battery without causing problems with modules/computers.


Like I said it was a thermostat that required alternator removal. All in all with walking trips to the parts store, for a lost 10mm nut, etc it was a 6 hour job.

Yeah I’ve got one but never used it but my understanding is to use a fresh battery and work quickly because you have minutes not hours.