2007 honda fit

Car shuts down while driving. Once it is jumped it runs for weeks then it happens again. If it’s the alternator it wouldn’t give me charging voltage. If it’s the battery it wouldn’t start. I have checked my voltages car off car on battery connected battery disconeccted. It’s my daughters car so I’m never there when it happens. When she brings it to me it seems to working fine.

The fit may have 2 battery systems, one battery for the starter motor, a different set for the car. Might be time for a new starter battery.

“The fit may have 2 battery systems”

In their quest for maximum MPGs, Honda equipped these cars with one tiny–barely adequate-- battery in order to cut the vehicle’s weight by a couple of pounds.

Two batteries in a Honda Fit?
I don’t think so!

Op writes …

I have checked my voltages car off car on battery connected battery disconeccted.

Your sentence isn’t 100% clear what you mean. But be sure to never run the engine with the battery disconnected. Doing so can cause all sorts of expensive to fix problems, including damaging the alternator, engine sensors, and the computer.

Have your daughter get a voltmeter like this:

It should show either 14 volts or 12.8 volts with the car running (Hondas have a dual-voltage system). If this is the original battery, put in a new one.

I also vote for a new battery if the charging voltage from the alternator checks out. I hear the batteries in these cars are not so great even when new.

The battery is eight years old anyway. It’s time to replace it anyway.

I too vote for replacing the battery, and make sure all the cable ends are clean and tight. Thewe batteries are vert small , expensive and used to be only sold by the dealer.
These batteries are so inadequate that there are u-tube videos on how to modify the car to accept a larger bttrery.

We’re heading into winter. Yes, replace the battery “proactively”. You won’t regret it.