Electric Question for MOTA Classic Holiday Christmas

[TonyAida]

Hello, I'm new to the form and thank you in advance for help and suggestions

 

I have a MOTA classic holiday christmas train, that I want to use for a decoration. 

it will have little to no weight on the containers (3 of them) but I do not like the way the train operates, it goes fast at the start with fresh batteries and slows down and dies or heats up and stops and when I left it cool down it runs again.

 

my question (if asked already please direct me to the post)

I want to slow down the train to a certain speed and make it last longest.

what is the best way to achieve this ? 

basically modify the train to last the longest possible time on a given battery 

it takes now 4 AA but I think I can easily modify it to put in 1 or 2 9v if needed. my main concern is last as long as possible at a constant speed. 

 

Thank you