Garmin GPS III Pilot - Memory battery problem.

Memory battery low warning at power up.

If my memory battery is fully charged (3v) and the GPS is left off for a couple of weeks then this message appears at next power up.

If the GPS is left off for more than a few days after that, all the way points are lost , also it does not know where it is in the world. This cannot be normal. All the Jeperson data is OK.

With a volt meter connected to the memory battery and the unit is turned on the memory battery starts to charge.

(2.56v after 1 hour)(2.76v after 3.5 hours)(2.94v after 24 hours)

If I turn it off the battery goes down , so definitely not being charged when in the powered off state.

Starting with no main battery and a flat memory battery 0.8v, I installed the main batteries which made no difference to the memory battery voltage.

The memory battery is 7maH 3v and the maximum charge is 0.5 ma or 500 ua , the maximum voltage is 3.5v so I will use a 3.3v , 3 terminal regulator and 4.7k limiting resistor.

The main battery voltage can be anywhere between 4.4v (Discharged) to 5.6v (Charged) so the 3.3v regulator should work well to get a small charge to the battery as well as supplying the memory.

Once I build it and work out what the total drain is I can tell how long the 1900mah Eneloop main batteries will last.

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