CX3-20f SPS problem

This morning I found this error in Navisphere:

"Standby Power Supply (Enclosure SPE SPS B) is faulted. The storage system will disable write cache.

Alert Code: 0x7404"

On the front of the SPE there is an amber light with an exclamation mark and on the back of the SPS B there are 2 amber lights, one corresponding to an exclamation mark and the other next to a crossed battery.

What does this mean, is the SPS B dead and needs replacing? The cable configuration hasn't changed

Thank you