Should a metal battery box be connected to Negative?

[Simon]

If it were to fail EMC as a system it would have nothing to do with the battery box. The machine would be producing the noise and would need the filtering to stop the noise getting up the cable. No change to the battery box would help.

[Siwastaja]

If it were to fail EMC as a system it would have nothing to do with the battery box. The machine would be producing the noise and would need the filtering to stop the noise getting up the cable. No change to the battery box would help.

Oh, don't be so sure, EMC is complex. BMS itself could fail radiated immunity or emissions for which grounded battery box could help. Or the machine conducting noise into supply cables which is then emitted by the larger loop within the battery, for which battery box could again help. But I agree that other means to filter out these problems should be exhausted first.

[Simon]

As you say any of these issues would not be a failure of the off the shelf battery and would need resolving at source.