That's the babies Super, I'm totally in love with the things, the downside is it looks like they may now be discontinued as the availability is a bit hit and miss, but on the plus side there are some great discounts to be had as Super Dude mentions. They have the individual cars discounted on Amazon.com to $4.99 each.
In case you're wondering Super the set you must have purchased was the 'Enforcer' set which is/was the largest set in the range and has two cars including the exclusive police car which is not available separately or in any other set at the moment.
On the plus side all the sets are compatible and can therefore expand your layout as much as you like, there are no restrictions on how many cars you have running simultaneously or any issues over voltages dropping over distance because as you mention the cars are self contained and powered by button cells
Personally I've managed to get one of each set (as each set has exclusive cars) and a handful of separate cars, my hope is to get an entire set before they disappear if they are discontinued...
In case you're wondering Super the set you must have purchased was the 'Enforcer' set which is/was the largest set in the range and has two cars including the exclusive police car which is not available separately or in any other set at the moment.
On the plus side all the sets are compatible and can therefore expand your layout as much as you like, there are no restrictions on how many cars you have running simultaneously or any issues over voltages dropping over distance because as you mention the cars are self contained and powered by button cells
Personally I've managed to get one of each set (as each set has exclusive cars) and a handful of separate cars, my hope is to get an entire set before they disappear if they are discontinued...