Do digital cameras generally have a time limit in Bulb mode?

In digital cameras, there are a few reasons for the limit:

1. The sensor does not integrate light as well as silver halide photography does, unless the sensor is cooled (which also improves "film" time exposures). There is a buildup of electronic noise, so that the image becomes unusable; see Image noise and Digital Camera Image Noise. During long exposures, some cameras can be set to take repeated short exposures and use an algorithm to reduce the average noise, but this takes a lot of processing power and therefore battery charge, and is not all that effective, in my experience.

2. As mentioned above, the battery drain and internal heating of the sensor can be excessive during a long exposure... and the hotter the sensor, the worse the noise.

Though film time exposures have their own limitations, such as reciprocity failure, I do have some nice 20-minute city-scape shots on Kodachrome, RIP, taken in very cold weather. There was danger of the emulsion cracking and static-discharge streaks, too, not to mention photographer frostbite.