The recharging cycle of NiMH batteries is a lot
more complex that just applying a voltage and
letting current flow into the batteries. Current
goes into the battery until the battery is fully charged
then the current drops off and the battery charger
should be turned off at that time. The Lionel charger does
not do that. The Lionel charger was designed by an outside
company for another purpose and not for NiMH batteries. That
charger will never work correctly.
The batteries Lionel sends with the Legacy, GP, are not very good.
Get rid of the GP batteries, turn off the charger and use Energizer
batteries and charger. That charger is not cheap,about $35 with batteries,
but it will charge only 3 batteries and then it turns off.