Looking for serial cable pin out for Rackmount UPS by APC

[tkamiya]

I have lots of rackmount UPS by APC.  They are all SMT series, SMT3000RM2U and SMT2200RM2U and such.  What I am looking for is a SERIAL cable for the UPS itself.  It is also different from consumer type UPS.  Please note, this is not same as serial cable for network plug in module, either.

The connector itself is a 10pin RJ-50 type.  Does anyone have a pin out for this? 
I'd like to update the firmware but this cable is rather expensive.  I'd like to make my own.

Thanks.

[Neomys Sapiens]

Look here:
https://pinoutguide.com/UPS/apc_0625_cable_pinout.shtml

[tkamiya]

That was very helpful.  Thank you very much.