I agree the instructions with the extended battery are poor. I presume the blue light comes on if the voltage supplied by the extended battery is high enough to charge the 2800, but the instructions say that the extended battery will not charge the 2800. As soon as the voltage drops below that level the blue light goes out but the 2800 continues to be powered by the extended battery. You can confirm this by checking the 2800 battery level after a few hours use - it will remain full until the external battery is exhausted, then the 2800 battery will start to be used. The only way to check if the external battery is exhausted is to plug it into the charger - a red light indicates it is discharged. Don't forget to switch the external battery off when charging both together. Only switch it on when the green light goes out: the blue light comes on followed by the green light as the extended battery voltage falls. When both lights go out, everything is charged.
Memeory MAp really should issue some better user guides for their stuff
Charge battery and the GPS, slide button to L, blue light comes on
Fire up GPS, works OK
After a while, 2-3 mins the blue light switches off.
Why? Is the battery still powering GPS, is GPS powering itself?
Re flick the bottom switch, blue light comes on again and same happens
Surely the blue light should stay constantly on so I know its powering the GPS?