The very bottom-left corner of the schematic for board v1.1 mentions the two charge rates, which you can control using solder jumper SJ15. Here’s the description of that jumper from the Jumper Settings page:
SJ15: Lipo battery charge rate: 500mA (default) or 1A. This jumper allows you to select the maximum charger output current of the onboard Lipo charger. Default setting is 500mA (solder jumper open). Add a solder bridge to increase the rate to 1A. Note that you’ll also need to close jumper SJ14 (set input limit to 1A) in order to get 1A charger output. This setting should only be changed if your input power source can supply more than 500mA. Setting the rate to 1A also causes the bq24074 charger chip to get extremely hot during charging, so use caution.
There are 2 solar panel jacks on the Mayfly v1.0 and v1.1. This was done to provide backwards-compatibility for older existing stations that still have the white JST plug soldered to the end of the solar panel extension cable. Since most people don’t want to have to solder things when assembling their kits, we switched to using the black quick-connect jack in 2021 so that people could simply insert the bare leads of the solar panel extension cable into the plug without having to solder anything. Only one solar panel jack should be used on a deployed station though. The 2 options are there just for convenience. Likewise, there are still 2 JST jacks labeled LIPO BATT, but users should only connect one battery at a time. The second jack is a legacy feature from many years ago when we used cellular boards that required a direct connection to the battery using a little double-ended JST cable. It will likely be removed from future Mayfly versions to eliminate confusion.