From 5f04140fe8c73a96bae2a4eba899f2b114849673 Mon Sep 17 00:00:00 2001
From: Lukas Lynch <madi@mxdi.xyz>
Date: Wed, 18 Feb 2026 16:20:25 -0800
Subject: [PATCH] Displays status/capacity for a dynamic # of batteries

---
 Makefile                 |  1 +
 components/dyn_battery.c | 80 ++++++++++++++++++++++++++++++++++++++++
 config.def.h             |  1 +
 slstatus.h               |  3 ++
 4 files changed, 85 insertions(+)
 create mode 100644 components/dyn_battery.c

diff --git a/Makefile b/Makefile
index 7a18274..d1b24dd 100644
--- a/Makefile
+++ b/Makefile
@@ -11,6 +11,7 @@ COM =\
 	components/cpu\
 	components/datetime\
 	components/disk\
+	components/dyn_battery\
 	components/entropy\
 	components/hostname\
 	components/ip\
diff --git a/components/dyn_battery.c b/components/dyn_battery.c
new file mode 100644
index 0000000..7f49122
--- /dev/null
+++ b/components/dyn_battery.c
@@ -0,0 +1,80 @@
+/* Written by Lukas Lynch <madi@mxdi.xyz> */
+/* Only Linux is supported */
+#include <stdio.h>
+#include <string.h>
+#include <dirent.h>
+
+/* extern char buf[n] */
+#include "../util.h"
+
+/* See components/battery.c */
+const char *battery_state(const char *);
+const char *battery_perc(const char *);
+
+/*
+* This output buffer is global so we can just return its address, instead of
+* copying its contents to 'buf' (declared in slstatus.c) with bprintf().
+*/
+char out[sizeof(buf)];
+
+#if defined(__linux__)
+#define BAT_PREFIX "BAT"
+#define BAT_PREFIX_LEN sizeof(BAT_PREFIX)-1 // NULL byte included in sizeof()
+#define BAT_DIR "/sys/class/power_supply/"
+
+/**
+* Displays the status and capacity of a dynamic amount of batteries (i.e.
+* laptops with external/secondary batteries).
+*
+* @param  fmt format string to use for each battery display. ordered key:
+*             %u: battery number || %s: battery state || %s battery capacity
+* @return address of the output buffer, which contains the status and
+*         capacities of all detected batteries
+*/
+const char *
+dyn_battery(const char *fmt) {
+    *out = '\0'; // Functionally "clears" the buffer after last run
+
+    DIR *dirp = opendir(BAT_DIR);
+    if(!dirp) {
+        fprintf(stderr, "dyn_battery: Failed to open %s\n", BAT_DIR);
+        return "err";
+    }
+
+    unsigned int outp = 0, // Next free position in 'out'
+                 batn = 0; // Battery # (i.e. BAT0, BAT1, ...)
+    struct dirent *fp;     // Current file in 'dirp' readout
+
+    while((fp = readdir(dirp))) {
+        char *bat = fp->d_name; // Makes following code less ugly
+
+        if(
+            strlen(bat) > BAT_PREFIX_LEN &&
+            strncmp(bat, BAT_PREFIX, BAT_PREFIX_LEN) == 0
+        ) {
+            outp += sprintf(
+                out + outp,         // Starts after previous writes
+                fmt,                // Format string specified in config.h
+                batn++,             // 'batn' is decoupled from OS BAT#
+                battery_state(bat), // See components/battery.c
+                battery_perc(bat)   // See components/battery.c
+            );
+
+            // Add space between battery entries
+            out[outp++] = ' ';
+        }
+    } // end while
+
+    if(closedir(dirp) != 0) {
+        fprintf(stderr, "dyn_battery: Failed to close %s.\n", BAT_DIR);
+        return "err";
+    }
+
+    if(*out) {
+        out[--outp] = '\0'; // Remove extra space after last write
+        return out;
+    } else return NULL;
+}
+#else // #if defined(__linux__)
+# error "dyn_battery: Only Linux is currently supported."
+#endif
\ No newline at end of file
diff --git a/config.def.h b/config.def.h
index 100093e..7f26909 100644
--- a/config.def.h
+++ b/config.def.h
@@ -26,6 +26,7 @@ static const char unknown_str[] = "n/a";
  * disk_perc           disk usage in percent           mountpoint path (/)
  * disk_total          total disk space in GB          mountpoint path (/)
  * disk_used           used disk space in GB           mountpoint path (/)
+ * dyn_battery         displays the name, state and    format string (%u, %s, %s)
  * entropy             available entropy               NULL
  * gid                 GID of current user             NULL
  * hostname            hostname                        NULL
diff --git a/slstatus.h b/slstatus.h
index 394281c..6beeaec 100644
--- a/slstatus.h
+++ b/slstatus.h
@@ -21,6 +21,9 @@ const char *disk_perc(const char *path);
 const char *disk_total(const char *path);
 const char *disk_used(const char *path);
 
+/* dyn_battery */
+const char *dyn_battery(const char *fmt);
+
 /* entropy */
 const char *entropy(const char *unused);
 
-- 
2.53.0