I don't have the T62B but only the T62C.
According to the
RK3026 thread it is possible to use newer ROMS from Energy Sistem Ereader Pro or C67ML BUT
only the system partition (if more than the system partition is flashed, touchscreen is reported to stop working). For the C67ML system.img you have to
adapt your boot.img to have a working backlight control. Those changes do not interfere with the Energy System Ereader Pro system.img, meaning if done well you can use ist with the other ROMs too. FOV has anounced a new C67ML port for Boyue (1.7.3). This will be a great ROM with good batterylife. But remember, extract only the system.img out of the ROM and flash it after having changed your boot.img. If you can't wait that long, create your own ROM out of the downloadable Energy Ereader Pro ROM version 4, extract and update it as
I described here with the Energy Ereader Pro update.zip version 5.
About the expectable batterylife (0,2% in sleep) I wrote something
there