I am aware of issue #1080.

Even with nothing connected to the converter, they use a large amount of power (2-4 MHe).

I recently played on the (admittedly very different) 1.12.2 version and this was not an issue, but I am aware that it's a different codebase. I just don't think this is entirely unfixable. I'm not sure if this helps debug it but hopefully it does.

Idea: is it not possible to code some sort of built-in "diode" style limit that limits the input HE to whatever the current output RF is? Essentially a dynamic version of the in-game diode that's built into the converter.

Converter loss was removed and replaced by a lowered efficiency for RF to HE converters, fixing the converter battery exploit.

Also next time please read the changelog

In fact now the two energy converters have a passive energy loss of 20% by default, causing at most 4MHE energy loss per second.
For now you can disable this loss by editing the config file /config/hbmConfig/hbmMachines.json, and the loss willbe off by default in the next release.

In fact now the two energy converters have a passive energy loss of 20% by default, causing at most 4MHE energy loss per second. For now you can disable this loss by editing the config file /config/hbmConfig/hbmMachines.json, and the loss willbe off by default in the next release.

This is with nothing connected to them. They should use 0 power. They instead use all of the available power. I connected one to a Spark storage block and it drew 5 MHe with nothing connected and the block fully charged.

That being said, you aren't far off. Disabling this setting by setting the decay value to 0.0 fixes the problem, so I guess that's where the problem lies. I'm guessing that's why this is disabled in the next release.