Can't turn on

May seem silly, but you don't say if the battery is fully charged.

might be a faulty battery, internal i've had this on a few gps's, battery needs just under 1 volt, but if there is lest than it can read on voltage it will not charge, you can try leaving it on charge for a few hours and see if it trickles in have has some that have take 3 hrs to start charging. once it takes hold of a charge it don't take long for it to be fully charged but leave it on for a bout 20 min off charger and charge again this should resort out the battery.

Even though it is fully charged you may need another battery?

turn salt system to 0 production and disconnect the black wire to the cell it will quit beeping

Remove the back and check and see if the battery isn't fully connected

Check to see if this is a power issue by connecting to shore power and fully charging your batteries overnight with instruments off. While still connected to shore power, with batteries fully charged, turn on C80 navigation system. If the loading screen comes on and does not reset, then try holding down the button immediately to the right of the red power button for at least 3 seconds to see if the system re-boots.

battery can fully charged but if contacts of the tray are dirt than no current can pass through. firstly check contacts, switch showing that it is come out, after pushing it in, also check for polirities of batteries.

has it gone into hibernation? ... try holding the power button down for 10 seconds

Mive did this. I left it in the computer for around 10 hours (the computer didnt seem to regonize it, but it still atttempted to charge) Then try and turn it on. It should work?

you need to charge a phone over night for the battery to fully charge and have a memory

try plugging in as charging and turn phone on by holding the red button down for a few seconds on the right hand side