Correct me if I'm wrong, but I wouldn't call the management engine (eg. HP iLO) the BIOS. Whilst those may support such warnings:

1) Not everyone wants to use iLO or whatever equivalent another OEM provides.

2) Whilst such systems do support sending warnings about system components via email, dashboards, etc. that doesn't mean they'll necessarily warn about a RAID controller's battery being depleted. If I remember correctly, iLO4 doesn't.

3) What about RAID cards like the P420 (*not* the P420i) that either aren't hooked up to a management engine or are from an entirely separate OEM?