docs: Priority Mode drives the first time slot, and correct the SPH slot names

Two gaps found via #388.

The firmware implements Priority Mode by toggling the enable bit of the first
slot for that mode, in the same second - Grid First Period 1 Enable (1082) for
Grid First. A reporter saw that entity change on its own, reasonably concluded
something was wrong, and opened an issue. It is documented now, with the
consequence that matters: the linked slot needs a 00:00-23:59 window or the mode
only applies inside whatever window is set.

Confirmed on an SPH 4.6E from HA's activity log across two cycles. The Battery
First linkage follows the same pattern and is marked expected, not confirmed.

Also: v1.6.7 renamed these entities and the docs still used the old names, so the
tables did not match the UI. The renaming makes the linkage legible - 'Period 7'
and 'Period 1' looked arbitrary; 'Grid First Period 1' and 'Battery First
Period 1' are obviously the first slot of each mode.

Flagged rather than fixed: the off-peak example pairs Grid First priority with a
Battery First window. That is what it has always said and may be correct, but it
has not been re-verified on hardware.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: 0xAHA

docs/controls/battery-scheduling.md

@@ -210,6 +210,37 @@ sets the global default:
 Time periods override this global default within defined windows. Periods use separate
 enable registers (not bit-packed like MOD).
 
+!!! warning "Priority Mode drives the first time slot — the firmware, not the integration"
+
+    Setting **Priority Mode** does not act alone. On SPH firmware the inverter implements it
+    by toggling the **enable bit of the first slot for that mode**, in the same second:
+
+    ```
+    08:00:37  Priority Mode                  -> Grid First
+    08:00:37  Grid First Period 1 Enable     -> Enabled
+    08:15:22  Priority Mode                  -> Load First
+    08:15:22  Grid First Period 1 Enable     -> Disabled
+    ```
+
+    | Priority Mode | Slot the firmware toggles | Register |
+    |---|---|---|
+    | Grid First | Grid First Period 1 Enable | 1082 |
+    | Battery First | Battery First Period 1 Enable | 1102 |
+
+    Two consequences:
+
+    - **That enable entity changing on its own is not a fault**, and not the Growatt cloud
+      overwriting you. It is the inverter doing what you asked.
+    - **Configure that first slot as `00:00`–`23:59`** and leave its enable alone. If the
+      window is narrow, or unset, the mode only takes effect inside that window — which
+      looks like Priority Mode being ignored at other times of day.
+
+    Confirmed on an SPH 4.6E (firmware RBBA060406/ZCBC-0006) from Home Assistant's own
+    activity log across two full cycles, reported on
+    [#388](https://github.com/0xAHA/Growatt_ModbusTCP/issues/388). The Grid First linkage is
+    directly observed; the Battery First one follows the same pattern and is expected rather
+    than confirmed.
+
 ![SPH time period layout](../images/sph-time-periods.svg)
 
 ### Available Time Period Entities
@@ -218,12 +249,16 @@ enable registers (not bit-packed like MOD).
 
 | Entity | Register | Purpose |
 |--------|----------|---------|
-| Time Period 1 Start / End | 1100, 1101 | AC charge window 1 |
-| Time Period 1 Enable | 1102 | Enable/disable slot 1 |
-| Time Period 2 Start / End | 1103, 1104 | AC charge window 2 |
-| Time Period 2 Enable | 1105 | Enable/disable slot 2 |
-| Time Period 3 Start / End | 1106, 1107 | AC charge window 3 |
-| Time Period 3 Enable | 1108 | Enable/disable slot 3 |
+| Battery First Period 1 Start / End | 1100, 1101 | Battery First window 1 |
+| Battery First Period 1 Enable | 1102 | Enable/disable slot 1 |
+| Battery First Period 2 Start / End | 1103, 1104 | Battery First window 2 |
+| Battery First Period 2 Enable | 1105 | Enable/disable slot 2 |
+| Battery First Period 3 Start / End | 1106, 1107 | Battery First window 3 |
+| Battery First Period 3 Enable | 1108 | Enable/disable slot 3 |
+
+> **Renamed in v1.6.7.** These displayed as "Time Period 1–3" and the Grid First slots below
+> as "Grid First Time Period 7–9", which matched neither the Growatt app nor the protocol.
+> Entity IDs are unchanged, so automations still work — only the displayed names moved.
 
 #### Battery First Extended Slots 4–6 (new in v0.6.8)
 
@@ -240,10 +275,10 @@ enable registers (not bit-packed like MOD).
 
 | Entity | Register | Purpose |
 |--------|----------|---------|
-| Grid First Time Period 4–6 Start/End | 1026–1033 | Grid First windows 4–6 |
-| Grid First Time Period 4–6 Enable | 1028, 1031, 1034 | Enable each slot |
-| Grid First Time Period 7–9 Start/End | 1080–1087 | Grid First windows 7–9 |
-| Grid First Time Period 7–9 Enable | 1082, 1085, 1088 | Enable each slot |
+| Grid First Period 4–6 Start/End | 1026–1033 | Grid First windows 4–6 |
+| Grid First Period 4–6 Enable | 1028, 1031, 1034 | Enable each slot |
+| Grid First Period 1–3 Start/End | 1080–1087 | Grid First windows 1–3 |
+| Grid First Period 1–3 Enable | 1082, 1085, 1088 | Enable each slot |
 
 > **SPH HU note:** The SPH 8000–10000 TL-HU uses a different holding register architecture.
 > Battery management registers (1044, 1070–1071, 1090–1108) return Modbus exceptions on HU
@@ -274,11 +309,18 @@ For each active slot:
 #### Example: Off-Peak Grid Charging (22:00–06:00)
 
 Set **Priority Mode** to `Grid First`, then:
-- Time Period 1 Start: `22:00`
-- Time Period 1 End: `06:00`
-- Time Period 1 Enable: `Enabled`
+- Battery First Period 1 Start: `22:00`
+- Battery First Period 1 End: `06:00`
+- Battery First Period 1 Enable: `Enabled`
 - All other periods: Disabled
 
+> **Check this against your own inverter before relying on it.** Registers 1100–1102 are the
+> *Battery First* slot 1, so this example pairs a Grid First priority with a Battery First
+> window. That combination is what was originally documented here and it may well be how SPH
+> firmware expects grid charging to be scheduled — but it has not been re-verified on
+> hardware since the slots were correctly named in v1.6.7. If your inverter behaves
+> differently, please say so on the issue tracker.
+
 ```yaml
 automation:
   - alias: "SPH — Arm off-peak grid charge"