The following information was obtained from the manufacturer's website (Juniper Systems).
Update Aug 2017 - If a Carlson RT3 will not recognize or charge the optional internal battery, you may need to perform a Hard Reset by holding the hardware Power button for more than 20 seconds (which electronically disconnects both batteries such as for storage), wait a few seconds, attach wall charger (which will electronically re-connect both batteries), and then briefly press the hardware Power button again (to begin boot sequence).
If a Carlson RT3 will not recognize or charge the main removable battery pack when inserted, verify if the unit will recognize a battery pack from another unit (if available). If not, check to verify that the "battery detect" magnet is still located on the inside of the battery compartment door as shown in the following image.
If this magnet is missing, you will need to obtain a new door. Please contact support@junipersys.com for assistance.
Otherwise, additional ideas may be provided in the following article.
KB# 1061, One or Both Batteries Of RT3 Tablet are Stuck at 7 Percent Charge
If this magnet is missing, you will need to obtain a new door. Please contact support@junipersys.com for assistance.
Otherwise, additional ideas may be provided in the following article.
