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Memory keeper

I have seen people recommend using a ‘memory keeper’ to save radio settings,etc. when disconnecting the cars battery, they seem to plug into power port (cigarette lighter to us older folks)…but my '09 Mazda 3’s ports are only live when the key is on run or accessory position. so do I leave the key on when disconnecting the car’s battery? doesn’t seem right to me, any thoughts?

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There’s also a version that plugs into the OBD port. That’s the one you’ll want if your power ports aren’t live when the car is off.

Better yet, here’s an example of one that works both ways:

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You can also hook up a 9V battery to the ends of the cables to the + and - terminals. As with any such setup, don’t have anything electric running, even a door-open light, when relying on the small battery.

No offense, but I kind of doubt that

My sister-in-law has a 2010 Mazda 3 and the power port is hot 24/7

I know this for a fact because I’ve verified it with a multimeter

It looks the accessory plug is for connecting the unit to an external power supply, not to plug into the car’s accessory outlet.

This might be adjustable. On my 2007 Town and Country van, it can be set to be always live. It depends on the position of its fuse inside the under-hood fuse box.

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Quite right, I missed that. Thanks for the correction.

I took an old 12 volt power supply for a printer, attached a power point socket, making sure the positive went to the center stud, you could do a permanent splice if desired for the obd connector.

If you have another good 12V battery, you could clamp jumpers from it to the + and - ends of the car’s cables. When you unhook the cables from the battery you are are replacing, that car still has a good strong power supply that won’t be bothered by a dome light or door open chime, etc.