Error indicators from the manual: - If the LEDs indicating battery status are all blinking, it means the charger is charging with insufficient power. - If LEDs indicating battery status are ON but not blinking, it means the charger is not charging (this may be due to low power or broken connection). - If the first, second, and fourth LEDs are OFF and only the third LED is ON, it means the temperature of the battery is out of range. - If the first, third, and fourth LEDs are OFF and only the second LED is ON, it means the charger's connection is failing. In regards to your first issue, it sounds like slot #1 is not charging, and slot #2 is charging but the battery is 75% full. Each solid LED equals 25% charge and the blinking LED means that charging is still occurring. When all LEDs are solid, the battery is fully charged. I'm unsure why the battery in slot #1 wouldn't be charging, but sometimes if you take the battery out and re-insert it it will restart the charging process. In regards to the second issue, that's the error code for the charger connection failing. Unfortunately that's all it says in the manual, so where the connection is failing is unclear. I would start with making sure the contacts on the battery are clean and free of debris and also make sure the pins inside each charger bay are clean and free of debris. Are you using the power adapter that was included with the charger? When two batteries are charging simultaneously it draws quite a bit of current, and if you are using a different power adapter it might not be able to provide the required current.