I think that I had to run the new battery flat a couple of times for the GPS to work out the capacity of the battery and give more accurate battery readings.
Thanks, apparently, it needs to be reset too, here is the info about resetting the Garmin Edge 800 Battery level indicator:
"Let the device drain the battery until it switches off (dies) as you did. The real battery level is zero at that point. Now the software of the device has to learn the new zero level. This can be achieved by doing
a full hard reset of the device immediately after it is connected to the charger. Do not skip this step. Regardless of when the battery indicator reaches 100% again, leave the device on the charger for at least 6 hours. This is to learn the device the real 100% charge level.
Device is ready to use now, but you will have to re-enter your settings because of the full reset. If in doubt if you have reached the ultimum with the battery indicator, you can repeat the whole re-cal procedure."
a full hard reset
"The procedure for a full factory reset using the buttons is (Source: Garmin)
- Turn device off, if not already off because of empty battery. And without cable connected.
- Hold Lap/Reset and Start/Stop (the front buttons)
- Press the Power button for a few seconds and and release.
- Continue to hold only Lap/Reset and Start/Stop.
- Release Lap/Reset and Start/Stop when the Garmin Logo is cleared.
- The unit will restart and clear non-vol. Now it will start the initial device setup starting with Language, etc..
If you are doing the procedure for calibration of the battery charge level indicator and have let the device drain its battery until it shuts down then it is important to connect the Edge to an external wall charger and not to a USB port on the PC. In this stage the device should not come into mass storage mode."
https://forums.garmin.com/sports-fi...265182/edge-explore-battery-meter-calibration