Insight required

[pfofit]

I assume that the problem is caused by the battery voltage falling as the engine is started. The battery probably falls to about 8 V during starting.

Probably not. If the battery drops below low 9's then the stater(provided its engages) will just go uggggh!

At 8 volts you'll be lucky to get the solenoid to even click, never mind getting the starter to turn.

I have seen voltages dip to 4V. That was on a Ford Transit, on the feed to the hazard warning lights, each time they flash.

Then you have a dead battery or one with a few bad cells my friend.
If a starter drawing 100-150 amps on #8 or smaller wire drags a batt to below 10 volts, there is no way a few lamps on #18 wire will drag a car battery down to 4 volts without vaporizing the wire harness, associated fuse and power distribution box from the many hundreds of amps that would flow to load down a car batt to that level.

Now if you replace the car batt with a half dozen energizer alkalines, then yes.

Now :
This GPS is being reset by a loss of power probably because of where the power is obtained from.

This GPS is not drawing 350ma on standby to maintain settings. If so then the batt would most likely be weak after sitting all night, let alone incapable of starting the car after a few days in a parking lot..

It most likely uses a few ma to maintain its parameters and the OP only needs to select/rewire a proper distribution point that does Not terminate when the key is turned to "start".

Playing with mega capacitors to compensate for a disconnection of power is a mega waste and poor design. What's gonna happen when the car won't start and you have to crank it for like 20 seconds or so. You'd have to give up half your trunk space to store the capacitor.

Rewire and your done.

cheers

 

[Hero999]

Another option is to use some small NiMH cells in a battery back up circuit that's on permanent charge.

 

[jpanhalt]

Every car I have seen in at least the past ten years has had an always-hot circuit. For example, the computer, alarm, and anti-theft radios don't reset when you start the car, but if you remove the negative terminal at the battery, at least some of them reset. So, I would look for the always-hot circuit.

A repair manual will tell you which circuit(s) stay hot. For example (Honda), the manual will say something like if you want to reset xyz, remove a certain fuse from the radio circuit. It happens to be the anti-theft circuit and in the 2000 Accord is located on the right side of the dash. You might even ask a good thief. I thnk the airbag circuit also stays hot, but I would be reluctant to mess with that too much.

John