So to upgrade the charger to automatically disconnect the battery once charging is completed I plan to add a MOSFET into the output line that is enabled by the charging in progress indicator.

In order to initiate charging a push button will allow a bypass to start the charging and to latch whilst charging is in progress.

The main parts are the high current / high power MOSFET capable of running in DC mode for the required current and voltage [SUP85N10] and the 5V regulator capable of being run off the high voltage 54.6V output [ZXTR2005ZQ]

The voltage of the indicator LED is only 2.23V so an additional transistor is needed to buffer the signal to drive the large MOSFET