Permanenty used SRAM for
global variables and local static variables. Without stack.
(This is just an overview and not byte-accurate)

ad_convertert:         22 Byte
battery_settings:      25 Byte
calibration_config:    41 Byte
  less useful: 20 Byte inverted
chargedischarge:       36 Byte
  less useful: 20 Byte sendbuffer
charging_delta_detect: 28 Byte
clock:                  4 Byte
control:               45 Byte
  less useful: 35 Byte selector data
da_output:              5 Byte
lcd:                   44 Byte
main:                   0 Byte
rs232_io:              20 Byte
  less useful: 15 Byte sendbuff
scheduler:             29 Byte
tools:                  0 Byte
user_in:               24 Byte
validator:             10 Byte (+12 if THREADBENCHMARK is enabled)

Sum:                  333 Byte

There may be some additional space used by the avr-libc
for the malloc function (not used) or errno.

The stack may use up to approx. 600 Byte, so there is not much space
left in the SRAM:
1024Byte-333Byte-600Byte= 91Byte free