Train too slow using rechargeable batteries

The toys are designed for 1.5V alkaline batteries which usually come out of the package with 1.7V and when flat reach 1.4V or lower.

Rechargeable batteries (NiMH) fully charged are around 1.35V and when discharged completely reach less than 1.25V.

I use NiMH rechargeable batteries.

-plarnold