I currently make acceleration depend on the fuel's energy. Wood has 2MJ, coal 4MJ, solid fuel 12MJ, rocket fuel 100MJ, nuclear 1210MJ. You can see this increases on an exponential scale. When you take the log10(energy), we actually arrive at quite nice values, resp: 0.3, 0.6, 1.0, 2.0, 3.0. These are the values I used as acceleration multipliers per fuel type. The electric battery does not have significantly more energy, and thus does not yield more acceleration.
In physics, it makes zero sense to relate energy and acceleration: acceleration should be based on power. However, the locomotive.max_power prototype-value is not available at runtime, hence this workaround. I'll investigate if/how I can hoist the max_power propertype value to the runtime, so I can use that as yet another multiplier.