A battery status program for x86-64 Linux laptops in the form of a 307-byte ELF executable.

$ btry
30.6 Wh / 31.1 Wh (98%)

Sometimes there are no energy_now and energy_full files, but charge_* files instead (at least on my ThinkPad X220). If this is the case, btry prints ampere hours instead of watt hours.

$ btry
2.2 Ah / 2.8 Ah (78%)

base64 -d <<< 'AAAAgAD//////////wA/kdbV/T4SKqi4gu7TNukZJeNdhjgGWjLCw6YYwm3tgKjiZLis8j
hz7+A+BEXQGjYrdisdU/fmh6I+bXFgKXsBP1Qihg6wueK0wKD1tL2vQRd8ZjmQi20OduGmiMyPyfsS2cSUUCK
SpQXtdHbQMRMn1UD6k/HrwFt3i+wzPNoG0tEHEZbJUTvdAVs0xS9PYrTTc4uSskePYWAK8t6VK/pmpItKsGnb
/qyGaIMl2/5TiqjHXTczFv3YkiNnJ7iqK8CtWhMwMlQxeyRuW3fpYgRKVPNKrX14kKobJSHZy4MuC9TE7lgYX
YJhBim5yRoO7wnYG3ezKX86Xvw/AFHGG8CTnD49szn/eHZAAA==' | unlzma > btry && chmod +x btry

• Anything that's not x86-64 and Linux is definitely not supported.
• I don't know how standard/portable the /sys/class/power_supply/BAT0 path used actually is.
• If neither an energy_full nor a charge_full file exists in /sys/class/power_supply/BAT0, an infinite loop results.
• Extra batteries (like in the ThinkPad T480) are ignored.

make

No.

When my ThinkPad X220 is plugged in at the time I wake it from suspend mode, I get the charge_now file. When it is not plugged in I get the energy_now file. At least I think that's how it works.