Describe the suggestion
Basically, in addition to the current two categories of internal combustion and steam, add in battery electric. A battery electric should have an internal "battery" that can store a certain amount of FE/RF, which can ONLY be charged via track augments (specifically a "charger" augment). Because there doesn't exist a "discharger" augment, then battery electric locos should keep their charge when broken and picked up as an item. Finally, battery electrics are instantly operable when you hit start (no warm up time) and cannot overheat (although if a temperature mechanic is included they might be less efficient at higher temperatures)

Applications of the suggestion
A straightforward way of making electric locomotives, fully realistic for battery electrics (which many people, myself included, have modelled). Also roughly the "standard" way of doing electric things in modded minecraft using FE/RF).