W211 ESP ABS Issue

[Ahmadtow]

I have problem with my E200 compressor 2003 its ABS light and ESP, i read about this issue, i get this:

Check break disk check voltage backup battary check SBC,

So the break disk is good and i dont know how to check SBC but i checked the voltage of backup battary and i think there are something wrong.

The backup battary when engine off is 12,6 and engine on the same 12,6

The main battary is 12,5 engine off and 13,6 engine on

So the backup battary have problem with charging,
Please need your kindly help