From 35b2b008c8cdd0344dec84fb628dd54dd94d1e86 Mon Sep 17 00:00:00 2001
From: Jakub <106778416+MarekZegare4@users.noreply.github.com>
Date: Sun, 10 May 2026 19:47:12 +0200
Subject: [PATCH] Battery %: use LiPo discharge curve with variable shutdown
 threshold

Replace linear voltage-to-percent formula with a LiPo discharge curve
lookup table and linear interpolation. The curve is then rescaled so
that low_batt_mv (configurable shutdown threshold) maps to 0% and
4200mV maps to 100%, preserving the non-linear shape regardless of
the chosen threshold.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 examples/companion_radio/ui-new/UITask.cpp | 35 +++++++++++++++++-----
 1 file changed, 28 insertions(+), 7 deletions(-)

diff --git a/examples/companion_radio/ui-new/UITask.cpp b/examples/companion_radio/ui-new/UITask.cpp
index 86ed9982..6381c7fe 100644
--- a/examples/companion_radio/ui-new/UITask.cpp
+++ b/examples/companion_radio/ui-new/UITask.cpp
@@ -558,13 +558,34 @@ class HomeScreen : public UIScreen {
 #ifndef BATT_MIN_MILLIVOLTS
   #define BATT_MIN_MILLIVOLTS 3200
 #endif
-#ifndef BATT_MAX_MILLIVOLTS
-  #define BATT_MAX_MILLIVOLTS 4200
-#endif
-    // 0% anchor: low_batt_mv if set, otherwise BATT_MIN_MILLIVOLTS
-    int minMv = (_node_prefs && _node_prefs->low_batt_mv > 0)
-                  ? (int)_node_prefs->low_batt_mv : BATT_MIN_MILLIVOLTS;
-    int pct = ((int)batteryMilliVolts - minMv) * 100 / (BATT_MAX_MILLIVOLTS - minMv);
+    // LiPo discharge curve: voltage (mV) → raw capacity (%)
+    static const struct { uint16_t mv; uint8_t pct; } CURVE[] = {
+      {3200,  0}, {3300,  3}, {3400,  8}, {3500, 15},
+      {3600, 25}, {3650, 33}, {3700, 45}, {3750, 58},
+      {3800, 68}, {3900, 77}, {4000, 86}, {4100, 93}, {4200, 100}
+    };
+    static const int CURVE_LEN = sizeof(CURVE) / sizeof(CURVE[0]);
+
+    auto curveAt = [&](int mv) -> int {
+      if (mv <= (int)CURVE[0].mv) return CURVE[0].pct;
+      if (mv >= (int)CURVE[CURVE_LEN-1].mv) return CURVE[CURVE_LEN-1].pct;
+      for (int i = 1; i < CURVE_LEN; i++) {
+        if (mv <= (int)CURVE[i].mv) {
+          int span_mv  = CURVE[i].mv  - CURVE[i-1].mv;
+          int span_pct = CURVE[i].pct - CURVE[i-1].pct;
+          return CURVE[i-1].pct + (mv - (int)CURVE[i-1].mv) * span_pct / span_mv;
+        }
+      }
+      return 100;
+    };
+
+    int low_mv = (_node_prefs && _node_prefs->low_batt_mv > 0)
+                   ? (int)_node_prefs->low_batt_mv : BATT_MIN_MILLIVOLTS;
+    int raw_pct = curveAt((int)batteryMilliVolts);
+    int low_pct = curveAt(low_mv);
+    // rescale so low_mv = 0% and 4200mV = 100%
+    int pct = (low_pct >= 100) ? 0
+              : (raw_pct - low_pct) * 100 / (100 - low_pct);
     if (pct < 0)   pct = 0;
     if (pct > 100) pct = 100;