diff --git a/src/Command/TestInvoiceManagerCommand.php b/src/Command/TestInvoiceManagerCommand.php
index 7feafcb9..6c971156 100644
--- a/src/Command/TestInvoiceManagerCommand.php
+++ b/src/Command/TestInvoiceManagerCommand.php
@@ -16,6 +16,7 @@ use App\Ramcar\ServiceType;
 
 use App\Entity\Battery;
 use App\Entity\CustomerVehicle;
+use App\Entity\Promo;
 
 class TestInvoiceManagerCommand extends Command
 {
@@ -66,7 +67,18 @@ class TestInvoiceManagerCommand extends Command
         $this->testBatterySalesTradeInQuantityNoDiscountWithoutTax();
 
         // battery sales with discount with tax
+        $this->testBatterySalesNoTradeInWithDiscountWithTax();
+
         // battery sales with discount without tax
+        $this->testBatterySalesNoTradeInWithDiscountWithoutTax();
+
+        // battery sales with discount and trade in with tax
+        $this->testBatterySalesTradeInSameBatteryWithDiscountWithTax();
+        $this->testBatterySalesTradeInDifferentBatteryWithDiscountWithTax();
+
+        // battery sales with discount and trade in without tax
+        $this->testBatterySalesTradeInSameBatteryWithDiscountWithoutTax();
+        $this->testBatterySalesTradeInDifferentBatteryWithDiscountWithoutTax();
 
         // battery replacement warranty with tax
         $this->testBatteryReplacementWarrantyWithTax();
@@ -126,8 +138,6 @@ class TestInvoiceManagerCommand extends Command
         $this->testTireRepairWithServiceFeeWithoutTax();
         $this->testTireRepairWithoutServiceFeeWithoutTax();
 
-        // TEST SCENARIO: new battery with discount
-        // TEST SCENARIO: new battery with discount and trade-in
         return 0;
     }
 
@@ -814,6 +824,278 @@ class TestInvoiceManagerCommand extends Command
         }
     } 
 
+    // battery sales with discount with tax
+    protected function testBatterySalesNoTradeInWithDiscountWithTax()
+    {
+        $criteria = new InvoiceCriteria();
+
+        // TEST SCENARIO: new battery, no trade-in, with discount, with tax
+        $criteria->setServiceType(ServiceType::BATTERY_REPLACEMENT_NEW);
+
+        $battery_id = 1038;
+        $battery = $this->em->getRepository(Battery::class)->find($battery_id);
+
+        $promo_id = 1;
+        $promo = $this->em->getRepository(Promo::class)->find($promo_id);
+
+        $criteria->addEntry($battery, null, 1);
+
+        $criteria->addPromo($promo);
+
+        $criteria->setIsTaxable();
+
+        $rules = $this->inv_manager->check($criteria);
+
+        // error_log(print_r($rules, true));
+
+        $invoice_data = $this->inv_manager->compute($criteria, $rules);
+
+        // error_log(print_r(json_encode($invoice_data), true));
+
+        foreach ($invoice_data as $data)
+        {
+            $invoice_items = $data['invoice_items'];
+            $total = $data['total'];
+            $promo = $data['promo'];
+
+            foreach ($invoice_items as $invoice_item)
+            {
+                error_log('TEST: ' . strtoupper(ServiceType::BATTERY_REPLACEMENT_NEW) . ' NO TRADE IN WITH DISCOUNT WITH TAX ' . $invoice_item->getTitle() . ' ' . $invoice_item->getQuantity() . ' ' . $invoice_item->getPrice());
+            }
+
+            error_log('PROMO ' . $promo->getName());
+
+            error_log('TOTAL ' . print_r(json_encode($total), true));
+        }
+    }
+
+    // battery sales with discount without tax
+    protected function testBatterySalesNoTradeInWithDiscountWithoutTax()
+    {
+        $criteria = new InvoiceCriteria();
+
+        // TEST SCENARIO: new battery, no trade-in, with discount, without tax
+        $criteria->setServiceType(ServiceType::BATTERY_REPLACEMENT_NEW);
+
+        $battery_id = 1038;
+        $battery = $this->em->getRepository(Battery::class)->find($battery_id);
+
+        $promo_id = 10;
+        $promo = $this->em->getRepository(Promo::class)->find($promo_id);
+
+        $criteria->addEntry($battery, null, 1);
+
+        $criteria->addPromo($promo);
+
+        $rules = $this->inv_manager->check($criteria);
+
+        // error_log(print_r($rules, true));
+
+        $invoice_data = $this->inv_manager->compute($criteria, $rules);
+
+        // error_log(print_r(json_encode($invoice_data), true));
+
+        foreach ($invoice_data as $data)
+        {
+            $invoice_items = $data['invoice_items'];
+            $total = $data['total'];
+            $promo = $data['promo'];
+
+            foreach ($invoice_items as $invoice_item)
+            {
+                error_log('TEST: ' . strtoupper(ServiceType::BATTERY_REPLACEMENT_NEW) . ' NO TRADE IN WITH DISCOUNT WITHOUT TAX ' . $invoice_item->getTitle() . ' ' . $invoice_item->getQuantity() . ' ' . $invoice_item->getPrice());
+            }
+
+            error_log('PROMO ' . $promo->getName());
+
+            error_log('TOTAL ' . print_r(json_encode($total), true));
+        }
+    }
+
+    // battery sales with discount and trade in with tax
+    protected function testBatterySalesTradeInSameBatteryWithDiscountWithTax()
+    {
+        $criteria = new InvoiceCriteria();
+
+        // TEST SCENARIO: new battery, no trade-in, with discount, with tax
+        $criteria->setServiceType(ServiceType::BATTERY_REPLACEMENT_NEW);
+
+        $battery_id = 1038;
+        $battery = $this->em->getRepository(Battery::class)->find($battery_id);
+
+        $promo_id = 1;
+        $promo = $this->em->getRepository(Promo::class)->find($promo_id);
+
+        $criteria->addEntry($battery, null, 1);
+
+        // add battery for trade in
+        $criteria->addEntry($battery, 'premium', 1);
+
+        $criteria->addPromo($promo);
+
+        $criteria->setIsTaxable();
+
+        $rules = $this->inv_manager->check($criteria);
+
+        // error_log(print_r($rules, true));
+
+        $invoice_data = $this->inv_manager->compute($criteria, $rules);
+
+        // error_log(print_r(json_encode($invoice_data), true));
+
+        foreach ($invoice_data as $data)
+        {
+            $invoice_items = $data['invoice_items'];
+            $total = $data['total'];
+            $promo = $data['promo'];
+
+            foreach ($invoice_items as $invoice_item)
+            {
+                error_log('TEST: ' . strtoupper(ServiceType::BATTERY_REPLACEMENT_NEW) . ' TRADE IN SAME BATTERY WITH DISCOUNT WITH TAX ' . $invoice_item->getTitle() . ' ' . $invoice_item->getQuantity() . ' ' . $invoice_item->getPrice());
+            }
+
+            error_log('PROMO ' . $promo->getName());
+
+            error_log('TOTAL ' . print_r(json_encode($total), true));
+        }
+    }
+
+    protected function testBatterySalesTradeInDifferentBatteryWithDiscountWithTax()
+    {
+        $criteria = new InvoiceCriteria();
+
+        // TEST SCENARIO: new battery, trade-in different battery, premium, with discount, with tax
+        $criteria->setServiceType(ServiceType::BATTERY_REPLACEMENT_NEW);
+
+        $battery_id = 1038;
+        $battery = $this->em->getRepository(Battery::class)->find($battery_id);
+
+        $promo_id = 1;
+        $promo = $this->em->getRepository(Promo::class)->find($promo_id);
+
+        // add battery
+        $criteria->addEntry($battery, null, 1);
+
+        $trade_battery_id = 1037;
+        $trade_battery = $this->em->getRepository(Battery::class)->find($trade_battery_id);
+
+        // add battery for trade in
+        $criteria->addEntry($trade_battery, 'premium', 1);
+
+        $criteria->addPromo($promo);
+
+        $criteria->setIsTaxable();
+
+        $rules = $this->inv_manager->check($criteria);
+
+        // error_log(print_r($rules, true));
+
+        $invoice_data = $this->inv_manager->compute($criteria, $rules);
+
+        foreach ($invoice_data as $data)
+        {
+            $invoice_items = $data['invoice_items'];
+            $total = $data['total'];
+
+            foreach ($invoice_items as $invoice_item)
+            {
+                error_log('TEST: ' . strtoupper(ServiceType::BATTERY_REPLACEMENT_NEW) . ' TRADE IN DIFFERENT BATTERY WITH DISCOUNT WITH TAX ' . $invoice_item->getTitle() . ' ' . $invoice_item->getQuantity() . ' ' . $invoice_item->getPrice());
+            }
+
+            error_log('TOTAL ' . print_r(json_encode($total), true));
+        }
+    }
+
+    // battery sales with discount and trade in without tax
+    protected function testBatterySalesTradeInSameBatteryWithDiscountWithoutTax()
+    {
+        $criteria = new InvoiceCriteria();
+
+        // TEST SCENARIO: new battery, no trade-in, with discount, with tax
+        $criteria->setServiceType(ServiceType::BATTERY_REPLACEMENT_NEW);
+
+        $battery_id = 1038;
+        $battery = $this->em->getRepository(Battery::class)->find($battery_id);
+
+        $promo_id = 1;
+        $promo = $this->em->getRepository(Promo::class)->find($promo_id);
+
+        $criteria->addEntry($battery, null, 1);
+
+        // add battery for trade in
+        $criteria->addEntry($battery, 'premium', 1);
+
+        $criteria->addPromo($promo);
+
+        $rules = $this->inv_manager->check($criteria);
+
+        // error_log(print_r($rules, true));
+
+        $invoice_data = $this->inv_manager->compute($criteria, $rules);
+
+        // error_log(print_r(json_encode($invoice_data), true));
+
+        foreach ($invoice_data as $data)
+        {
+            $invoice_items = $data['invoice_items'];
+            $total = $data['total'];
+            $promo = $data['promo'];
+
+            foreach ($invoice_items as $invoice_item)
+            {
+                error_log('TEST: ' . strtoupper(ServiceType::BATTERY_REPLACEMENT_NEW) . ' TRADE IN SAME BATTERY WITH DISCOUNT WITHOUT TAX ' . $invoice_item->getTitle() . ' ' . $invoice_item->getQuantity() . ' ' . $invoice_item->getPrice());
+            }
+
+            error_log('PROMO ' . $promo->getName());
+
+            error_log('TOTAL ' . print_r(json_encode($total), true));
+        }
+    }
+
+    protected function testBatterySalesTradeInDifferentBatteryWithDiscountWithoutTax()
+    {
+        $criteria = new InvoiceCriteria();
+
+        // TEST SCENARIO: new battery, trade-in different battery, premium, with discount, without tax
+        $criteria->setServiceType(ServiceType::BATTERY_REPLACEMENT_NEW);
+
+        $battery_id = 1038;
+        $battery = $this->em->getRepository(Battery::class)->find($battery_id);
+
+        $promo_id = 1;
+        $promo = $this->em->getRepository(Promo::class)->find($promo_id);
+
+        // add battery
+        $criteria->addEntry($battery, null, 1);
+
+        $trade_battery_id = 1037;
+        $trade_battery = $this->em->getRepository(Battery::class)->find($trade_battery_id);
+
+        // add battery for trade in
+        $criteria->addEntry($trade_battery, 'premium', 1);
+
+        $criteria->addPromo($promo);
+
+        $rules = $this->inv_manager->check($criteria);
+
+        // error_log(print_r($rules, true));
+
+        $invoice_data = $this->inv_manager->compute($criteria, $rules);
+
+        foreach ($invoice_data as $data)
+        {
+            $invoice_items = $data['invoice_items'];
+            $total = $data['total'];
+
+            foreach ($invoice_items as $invoice_item)
+            {
+                error_log('TEST: ' . strtoupper(ServiceType::BATTERY_REPLACEMENT_NEW) . ' TRADE IN DIFFERENT BATTERY WITH DISCOUNT WITHOUT TAX ' . $invoice_item->getTitle() . ' ' . $invoice_item->getQuantity() . ' ' . $invoice_item->getPrice());
+            }
+
+            error_log('TOTAL ' . print_r(json_encode($total), true));
+        }
+    }
+
     // battery replacement warranty with tax 
     protected function testBatteryReplacementWarrantyWithTax()
     {
diff --git a/src/Invoice/DiscountType.php b/src/Invoice/DiscountType.php
index a1bea802..091ff9c6 100644
--- a/src/Invoice/DiscountType.php
+++ b/src/Invoice/DiscountType.php
@@ -42,15 +42,44 @@ class DiscountType implements InvoiceInterface
         switch ($apply_to)
         {
             case DiscountApply::SRP:
-                $discount = round($total['sell_price'] * $rate, 2);
+                $discount = bcmul($total['sell_price'], $rate, 2);
                 break;
             case DiscountApply::OPL:
                 // $discount = round($total['sell_price'] * 0.6 / 0.7 * $rate, 2);
-                $discount = round($total['sell_price'] * (1 - 1.5 / 0.7 * $rate), 2);
+                // $discount = round($total['sell_price'] * (1 - 1.5 / 0.7 * $rate), 2);
+                $num1 = bcdiv(1.5, 0.7, 9);
+                $num1_rate = bcmul($num1, $rate, 9);
+                $multiplier = bcsub(1, $num1_rate, 9);
+
+                $discount = bcmul($total['sell_price'], $multiplier, 2);
                 break;
         }
 
+        // if discount is higher than 0, add to items
+        if ($discount > 0)
+        {
+            $qty = 1;
+            $price = bcmul(-1, $discount, 2);
+
+            $items[] = [
+                'promo' => $promo,
+                'title' => $this->getTitle(),
+                'qty' => $qty,
+                'price' => $price,
+            ];
+        }
+
+        $total['discount'] = $discount;
+        $total['total_price'] = bcsub($total['total_price'], $discount, 2);
+
         return $items;
     }
+
+    protected function getTitle()
+    {
+        $title = 'Promo discount';
+
+        return $title;
+    }
 }
 
diff --git a/src/Service/InvoiceManager.php b/src/Service/InvoiceManager.php
index b1baf521..8743a099 100644
--- a/src/Service/InvoiceManager.php
+++ b/src/Service/InvoiceManager.php
@@ -162,10 +162,15 @@ class InvoiceManager
                 {
                     if (isset($active_rules['discount_type']))
                     {
-                        $discount_items = $active_rules['discount_type']->compute($criteria, $stype_fees);
+                        $discount_items = $active_rules['discount_type']->compute($criteria, $stype_fees, $total);
+                        foreach ($discount_items as $discount_item)
+                        {
+                            $items[] = $discount_item;
+                        }
                     }
                 }
 
+                $promo = null;
                 foreach ($items as $item)
                 {
                     $invoice_item = new InvoiceItem();
@@ -177,11 +182,15 @@ class InvoiceManager
                     if (isset($item['battery']))
                         $invoice_item->setBattery($item['battery']);
 
+                    if (isset($item['promo']))
+                        $promo = $item['promo'];
+
                     $invoice_items[] = $invoice_item;
                 }
 
-                // also need to return the total
+                // also need to return the total and the promo
                 $data[] = [
+                    'promo' => $promo,
                     'invoice_items' => $invoice_items,
                     'total' => $total,
                 ];