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The red light in the battery compartment dims to a very low intensity, followed by a blinking orange light during charging. The manual does not clearly explain what this indicates.

The display reads "bat chrg," but it's unclear if this signifies normal charging, nearing full charge, or a potential issue.

It seems you are referring to the new LP2 circuit. It will charge whenever USB is connected. Power modes are off, on, on+wl

Charge current is small. Charging can be done from any USB jack, including computers.

There is no orange light on the charge board. This is the Teensy light you are referring to.

You might be confused what’s what in the instrument. In the LP2 there is no light at all in the battery compartment, so you are probably referring to the main electronics compartment in there. And there are a few lights in there. The LiPo charge board is placed on the front wall of the main compartment, and it has just one LED. It is red and it glows when charging and goes off when fully charged.

All indications of charging percentages, charge status and voltage levels are approximate based on incoming voltage levels to the Teensy. So, if the battery accepts charge, voltage goes up to about 4.0–4.1V and charge light goes off it is ok and full even if the info screen should say 90%. This is probably not the thing here, but it is still good to know.

So, .. based upon your description, it is possible for a NuEVI to show indication that the battery is only at 90% (but the charging light is off, indicating that it is fully charged?) ... so you go by the charging light as opposed to the menu item indicating % charged?

Yes, the charging light is the one to go by to see if the charge is complete or not.