diff --git a/backend/services/planning_engine.py b/backend/services/planning_engine.py
index 4aa6f53..3cd1316 100644
--- a/backend/services/planning_engine.py
+++ b/backend/services/planning_engine.py
@@ -159,10 +159,19 @@ def _select_charge_slots(
     current_soc_wh: float,
 ) -> set[int]:
     """
-    Pre-select which slots are eligible for battery charging.
-    Only the X cheapest sell-price PV-surplus slots are selected,
-    enough to fill the battery with a configurable buffer.
-    Returns set of slot indices.  Empty set = no restriction.
+    Pre-select which slots are eligible for battery charging (anti-micro-cycling).
+
+    Logika:
+      1) Sloty s PV-surplus (pv_a + pv_b > load_baseline) jsou vždy zahrnuty –
+         jde o „zdarma“ nabíjení z FVE, nemá smysl ho zakazovat.
+      2) Zbývající energetický rozpočet (cíl = charge_buf × (soc_max − current_soc),
+         snížený o očekávaný přínos z PV-surplus slotů) se doplní nejlevnějšími sloty
+         podle buy_price (nákupní cena ze sítě).
+      3) Per-slot kapacita přírůstku SoC = max_charge_power × η × 15 min (plný výkon,
+         ne limitovaný aktuálním PV-surplus výkonem).
+
+    Vrací množinu indexů povolených pro `bc[t] > 0` v MILP. Prázdná množina = žádné
+    restrikce.  `charge_slot_buffer <= 0` v DB ⇒ všechny sloty povoleny.
     """
     charge_buf = float(getattr(battery, "charge_slot_buffer", 0) or 0)
     if charge_buf <= 0:
@@ -172,28 +181,35 @@ def _select_charge_slots(
     if energy_to_fill <= 0:
         return set()
 
-    candidates: list[tuple[int, float, float]] = []
-    for t, s in enumerate(slots):
-        pv_surplus = max(0, s.pv_a_forecast_w + s.pv_b_forecast_w - s.load_baseline_w)
-        if pv_surplus <= 0:
-            continue
-        charge_w = min(float(battery.max_charge_power_w), float(pv_surplus))
-        charge_wh = charge_w * float(battery.charge_efficiency) * INTERVAL_H
-        candidates.append((t, float(s.sell_price), charge_wh))
-
-    candidates.sort(key=lambda x: x[1])
+    eta = float(getattr(battery, "charge_efficiency", 1.0) or 1.0)
+    max_p_w = float(getattr(battery, "max_charge_power_w", 0.0) or 0.0)
+    per_slot_full_wh = max_p_w * eta * INTERVAL_H
 
     selected: set[int] = set()
+    pv_budget_wh = 0.0
+    for t, s in enumerate(slots):
+        pv_surplus_w = max(0, s.pv_a_forecast_w + s.pv_b_forecast_w - s.load_baseline_w)
+        if pv_surplus_w <= 0:
+            continue
+        selected.add(t)
+        pv_budget_wh += min(float(pv_surplus_w), max_p_w) * eta * INTERVAL_H
+
+    target_wh = energy_to_fill * charge_buf
+    remaining_wh = max(0.0, target_wh - pv_budget_wh)
+    if remaining_wh <= 0 or per_slot_full_wh <= 0:
+        return selected
+
+    grid_candidates = [
+        (t, float(s.buy_price)) for t, s in enumerate(slots) if t not in selected
+    ]
+    grid_candidates.sort(key=lambda x: x[1])
+
     cumulative = 0.0
-    target = energy_to_fill * charge_buf
-    for t, _price, wh in candidates:
-        if cumulative >= target:
+    for t, _price in grid_candidates:
+        if cumulative >= remaining_wh:
             break
         selected.add(t)
-        cumulative += wh
-
-    if cumulative < energy_to_fill:
-        selected = set(c[0] for c in candidates)
+        cumulative += per_slot_full_wh
 
     return selected
 
diff --git a/backend/tests/test_planning_charge_slot_selection.py b/backend/tests/test_planning_charge_slot_selection.py
new file mode 100644
index 0000000..0166343
--- /dev/null
+++ b/backend/tests/test_planning_charge_slot_selection.py
@@ -0,0 +1,128 @@
+"""`_select_charge_slots`: pre-selection nabíjecích slotů (anti-micro-cycling).
+
+Ověřuje novou logiku podle varianty B:
+  - PV-surplus sloty jsou vždy zahrnuty.
+  - Zbytek rozpočtu doplnit nejlevnějšími sloty podle `buy_price` (ne `sell_price`).
+  - Žádné sloty nesmí být vyloučeny kvůli tomu, že nemají PV-surplus, když
+    `charge_slot_buffer` > 0 a ještě chybí energie do `soc_max`.
+"""
+
+from __future__ import annotations
+
+import unittest
+from datetime import datetime, timezone
+from types import SimpleNamespace
+
+from services.planning_engine import INTERVAL_H, PlanningSlot, _select_charge_slots
+
+
+def _slot(*, buy: float, sell: float = 1.0, pv: int = 0, load: int = 2_000) -> PlanningSlot:
+    return PlanningSlot(
+        interval_start=datetime(2026, 4, 19, 12, 0, tzinfo=timezone.utc),
+        buy_price=buy,
+        sell_price=sell,
+        pv_a_forecast_w=0,
+        pv_b_forecast_w=pv,
+        load_baseline_w=load,
+        ev1_connected=False,
+        ev2_connected=False,
+    )
+
+
+def _battery(
+    *,
+    charge_buf: float = 1.3,
+    uc_wh: float = 64_000.0,
+    soc_max_pct: float = 95.0,
+    max_charge_w: float = 18_000.0,
+    charge_eff: float = 0.95,
+) -> SimpleNamespace:
+    return SimpleNamespace(
+        usable_capacity_wh=uc_wh,
+        soc_max_wh=soc_max_pct / 100.0 * uc_wh,
+        max_charge_power_w=max_charge_w,
+        charge_efficiency=charge_eff,
+        charge_slot_buffer=charge_buf,
+    )
+
+
+class SelectChargeSlotsTests(unittest.TestCase):
+    def test_buffer_zero_returns_all_slots(self) -> None:
+        slots = [_slot(buy=3.0) for _ in range(4)]
+        battery = _battery(charge_buf=0.0)
+        out = _select_charge_slots(slots, battery, current_soc_wh=0.0)
+        self.assertEqual(out, set(range(4)))
+
+    def test_pv_surplus_slot_always_selected_regardless_of_buy_price(self) -> None:
+        """Slot s PV-surplus má být in, i když má nejvyšší buy_price."""
+        slots = [
+            _slot(buy=0.5, pv=0, load=2_000),          # bez PV, levný grid
+            _slot(buy=9.9, pv=8_000, load=2_000),      # velký PV-surplus, drahý grid
+        ]
+        battery = _battery()
+        out = _select_charge_slots(slots, battery, current_soc_wh=0.0)
+        self.assertIn(1, out)
+
+    def test_grid_filler_prefers_lowest_buy_price(self) -> None:
+        """Mezi neprvními sloty se vybere ten s nejnižší buy_price."""
+        slots = [
+            _slot(buy=3.0, pv=0, load=2_000, sell=0.1),
+            _slot(buy=0.4, pv=0, load=2_000, sell=0.3),
+            _slot(buy=1.2, pv=0, load=2_000, sell=0.2),
+        ]
+        battery = _battery(
+            charge_buf=1.3, uc_wh=64_000.0, soc_max_pct=95.0, max_charge_w=18_000.0
+        )
+        out = _select_charge_slots(slots, battery, current_soc_wh=0.0)
+        self.assertIn(1, out)
+
+    def test_does_not_exclude_slot_just_because_pv_below_load(self) -> None:
+        """Regrese: dřívější logika vyřazovala sloty bez PV-surplus úplně."""
+        slots = [
+            _slot(buy=0.4, pv=3_320, load=3_747),
+            _slot(buy=0.42, pv=2_116, load=3_747),
+            _slot(buy=0.44, pv=1_649, load=3_747),
+            _slot(buy=0.47, pv=1_276, load=3_747),
+            _slot(buy=1.13, pv=1_286, load=523),
+            _slot(buy=1.60, pv=1_020, load=523),
+        ]
+        battery = _battery()
+        out = _select_charge_slots(slots, battery, current_soc_wh=0.2 * battery.usable_capacity_wh)
+        for idx in (0, 1, 2, 3):
+            self.assertIn(
+                idx,
+                out,
+                msg=(
+                    f"Slot {idx} (levný grid nákup ~0.4 Kč) musí být povolen pro "
+                    "nabíjení i bez PV-surplus, jinak optimizer skončí s dražším "
+                    "nákupem v pozdějších slotech (nelogická ekonomika)."
+                ),
+            )
+
+    def test_energy_budget_is_charge_buf_times_headroom(self) -> None:
+        """Součet uvolněné energie se pohybuje okolo charge_buf × (soc_max − current_soc)."""
+        slots = [_slot(buy=float(i + 1), pv=0, load=2_000) for i in range(40)]
+        battery = _battery(
+            charge_buf=1.3, uc_wh=64_000.0, soc_max_pct=95.0, max_charge_w=18_000.0
+        )
+        current_soc_wh = 0.2 * battery.usable_capacity_wh
+        target = battery.charge_slot_buffer * (battery.soc_max_wh - current_soc_wh)
+        per_slot_wh = (
+            battery.max_charge_power_w * battery.charge_efficiency * INTERVAL_H
+        )
+        out = _select_charge_slots(slots, battery, current_soc_wh=current_soc_wh)
+        slots_picked = len(out)
+        self.assertLessEqual((slots_picked - 1) * per_slot_wh, target)
+        self.assertGreaterEqual(slots_picked * per_slot_wh, target)
+
+    def test_returns_empty_when_battery_is_full(self) -> None:
+        slots = [_slot(buy=0.1) for _ in range(3)]
+        battery = _battery()
+        out = _select_charge_slots(
+            slots, battery, current_soc_wh=battery.soc_max_wh + 1.0
+        )
+        self.assertEqual(out, set())
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/docs/04-modules/modbus-registers.md b/docs/04-modules/modbus-registers.md
index 12d51b9..0ef4253 100644
--- a/docs/04-modules/modbus-registers.md
+++ b/docs/04-modules/modbus-registers.md
@@ -60,7 +60,7 @@ Režim **CHARGE_CHEAP** v EMS nastaví `grid_setpoint_w` tak, aby platila podmí
 
 ### Čtyři typy slotů a mapování na registry
 
-Solver předvybírá sloty pro nabíjení a export-vybíjení (`_select_charge_slots`, `_select_discharge_export_slots`). Výsledné setpointy pak určují typ slotu:
+Solver předvybírá sloty pro nabíjení a export-vybíjení (`_select_charge_slots`, `_select_discharge_export_slots`). Nabíjení: vždy povoleno v slotech s PV-surplus; zbytek rozpočtu (`charge_slot_buffer × (soc_max − current_soc) − PV přínos`) doplněn nejlevnějšími sloty podle **`buy_price`** (nákupní cena ze sítě). Export-vybíjení: top-N slotů podle nejvyšší **`sell_price`**. Výsledné setpointy pak určují typ slotu:
 
 | | **Charge** | **Pass-through** | **Discharge-export** | **Self-consumption** |
 |---|---|---|---|---|