My laptop battery informations was placed in /sys/class/power_supply/CMB0. But battery.el try to find only /sys/class/power_supply/BAT% series. So display-battery-mode does not show any battery informations. Please consider existing different information directories.
In GNU Emacs 24.5.1 (x86_64-pc-linux-gnu, GTK+ Version 3.18.9) of 2016-04-18 on lgw01-04, modified by Debian Windowing system distributor `The X.Org Foundation', version 11.0.11804000 System Description: elementary OS 0.4 Loki
Important settings: value of $LC_MONETARY: ko_KR.UTF-8 value of $LC_NUMERIC: ko_KR.UTF-8 value of $LC_TIME: ko_KR.UTF-8 value of $LANG: ko_KR.UTF-8 value of $XMODIFIERS: locale-coding-system: utf-8-unix
Major mode: Org
Minor modes in effect: org-indent-mode: t override-global-mode: t electric-indent-mode: t mouse-wheel-mode: t file-name-shadow-mode: t global-font-lock-mode: t font-lock-mode: t auto-composition-mode: t auto-encryption-mode: t auto-compression-mode: t column-number-mode: t line-number-mode: t global-visual-line-mode: t visual-line-mode: t transient-mark-mode: t
Recent messages: ESC <mouse-1> is undefined Entering debugger... Making completion list... [8 times] Type "q" in help window to restore its previous buffer. Making completion list...
Making completion list... [3 times]
Making completion list... [3 times] call-interactively: End of buffer [4 times]