MagSafe Charger firmware version 247 (10M229) has been made available by Apple, though there are no known user-facing changes.
Apple released a MagSafe Charger firmware update The MagSafe Charger is a simple device with some on-device intelligence for charging the iPhone at specific rates given certain information provided by the connection. Apple doesn't provide release notes for MagSafe Charger firmware updates so expect bug fixes and optimization.
The previous firmware version was 174 (9M5069), and the new version is 247 (10M229).
The new firmware is installed automatically for users, with no mechanism available to manually force an update. As long as the MagSafe Charger is connected to power and your iPhone the update should -- eventually -- install automatically.
MagSafe Charger owners can check the current firmware for their device within the Settings app.
How to check your MagSafe Charger firmware version
MagSafe Charger firmware update now available