Hi Juan,
        using the -s sensor option for envstat, I see the following:

galant: {1} envstat
    acpiacad0 connected:         ON
       acpibat0 present:         ON
    acpibat0 design cap:      4.500 Ah
 acpibat0 last full cap:      4.500 Ah
    acpibat0 technology:          1
acpibat0 design voltage:     10.800 V
      acpibat0 warn cap:      0.090 Ah ( 2.00%)
       acpibat0 low cap:      0.000 Ah ( 0.00%)
       acpibat0 voltage:     11.300 V
   acpibat0 charge rate:        N/A
acpibat0 discharge rate:        N/A
        acpibat0 charge:      4.500 Ah (100.00%)
      acpibat0 charging:        OFF
  acpibat0 charge state:     NORMAL
       acpibat1 present:        OFF
    acpibat1 design cap:      0.000 Wh
 acpibat1 last full cap:      0.000 Wh
    acpibat1 technology:          0
acpibat1 design voltage:      0.000 V
      acpibat1 warn cap:      0.000 Wh
       acpibat1 low cap:      0.000 Wh
       acpibat1 voltage:      0.000 V
   acpibat1 charge rate:      0.000 W
acpibat1 discharge rate:      0.000 W
        acpibat1 charge:      0.000 Wh
      acpibat1 charging:        OFF
  acpibat1 charge state:    UNKNOWN
    acpitz0 temperature:     64.000 degC

galant: {2} envstat -d acpibat0
       acpibat0 present:         ON
    acpibat0 design cap:      4.500 Ah
 acpibat0 last full cap:      4.500 Ah
    acpibat0 technology:          1
acpibat0 design voltage:     10.800 V
      acpibat0 warn cap:      0.090 Ah ( 2.00%)
       acpibat0 low cap:      0.000 Ah ( 0.00%)
       acpibat0 voltage:     11.300 V
   acpibat0 charge rate:        N/A
acpibat0 discharge rate:        N/A
        acpibat0 charge:      4.500 Ah (100.00%)
      acpibat0 charging:        OFF
  acpibat0 charge state:     NORMAL

galant: {3} envstat -d acpibat0 -s 'design cap'
envstat: unknown sensor `design cap' for device `acpibat0'

galant: {4} envstat -d acpibat0 -s 'acpibat0 design cap'
    acpibat0 design cap:      4.500 Ah

is this a bug?

I'm not sure what the intention here is: the name of the sensor seems to
contain the name of the device, but although this is done in dev/acpi when
registering the sensors, it seems that envstat(1) does not print the name
of the device separately in any case .. should it?

regards,
iain