diff --git a/minigrid/device_interface.py b/minigrid/device_interface.py
index 6d256b0..9d97d9d 100644
--- a/minigrid/device_interface.py
+++ b/minigrid/device_interface.py
@@ -6,6 +6,8 @@
 from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
 from cryptography.hazmat.backends import default_backend
 
+from sqlalchemy.dialects.postgresql import insert
+
 import minigrid.models as models
 
 
@@ -221,18 +223,22 @@ def write_credit_card(
         naive_payload[94:96],
         bytes(13),
         (sum(naive_payload[94:96]) & 0xFF).to_bytes(1, 'big'),
-        bytes(32),  # maybe more?
     ))
     cache.set('device_info', _wrap_binary(actual_payload), 5)
+    data = {
+        'credit_card_id': str(credit_card_id),
+        'credit_minigrid_id': minigrid_id,
+        'credit_amount': credit_amount,
+        'credit_day_tariff': day_tariff,
+        'credit_day_tariff_start': day_tariff_start,
+        'credit_night_tariff': night_tariff,
+        'credit_night_tariff_start': night_tariff_start,
+        'credit_tariff_creation_timestamp': tariff_creation_timestamp,
+        'credit_tariff_activation_timestamp': tariff_activation_timestamp,
+    }
+    statement = (
+        insert(models.CreditCardHistory)
+        .values(**data)
+        .on_conflict_do_nothing())
     with models.transaction(session) as tx_session:
-        tx_session.add(models.CreditCardHistory(
-            credit_card_id=credit_card_id,
-            credit_minigrid_id=minigrid_id,
-            credit_amount=credit_amount,
-            credit_day_tariff=day_tariff,
-            credit_day_tariff_start=day_tariff_start,
-            credit_night_tariff=night_tariff,
-            credit_night_tariff_start=night_tariff_start,
-            credit_tariff_creation_timestamp=tariff_creation_timestamp,
-            credit_tariff_activation_timestamp=tariff_activation_timestamp,
-        ))
+        tx_session.execute(statement)
diff --git a/minigrid/handlers.py b/minigrid/handlers.py
index d30ba9f..79baa6b 100644
--- a/minigrid/handlers.py
+++ b/minigrid/handlers.py
@@ -633,7 +633,10 @@ def _user_or_maintenance_card(binary):
 def _credit_card(session, cipher, binary, credit_card_id):
     result = OrderedDict()
     #result[3] = _decrypt(cipher, unhexlify(binary[131:195])).hex()  # contains tariff information
-    sector_4 = unhexlify(binary[196:]).rstrip(b'\x00')
+    raw_sector_4 = unhexlify(binary[196:])
+    if not any(raw_sector_4):
+        return result
+    sector_4 = raw_sector_4.split(b'###')[0][:-2]
     # If card has been used...
     record_timestamp = datetime.fromtimestamp(
         int(sector_4[4:14].decode('ascii'))).isoformat()
@@ -762,7 +765,7 @@ def post(self):
                 # TODO: clean this up
                 payload = _pack_into_dict(self.session, body)
             except Exception as error:
-                cache.set('card_read_error', str(error))
+                cache.set('card_read_error', str(error), 5)
             else:
                 cache.set('received_info', payload, 5)
                 cache.delete('card_read_error')
diff --git a/minigrid/models.py b/minigrid/models.py
index 18c2771..4f0dd71 100644
--- a/minigrid/models.py
+++ b/minigrid/models.py
@@ -222,7 +222,7 @@ class SystemHistory(Base):
         sa.CheckConstraint('sh_meter_id > 0'), nullable=False)
     sh_meter_energy_usage = sa.Column(
         pg.INTEGER,
-        sa.CheckConstraint('sh_meter_energy_usage > 0'), nullable=False)
+        sa.CheckConstraint('sh_meter_energy_usage >= 0'), nullable=False)
     sh_meter_credit = sa.Column(
         pg.INTEGER,
         sa.CheckConstraint('sh_meter_credit >= 0'), nullable=False)
diff --git a/prod/docker-compose.yml b/prod/docker-compose.yml
index b3c181b..b33b98f 100644
--- a/prod/docker-compose.yml
+++ b/prod/docker-compose.yml
@@ -1,7 +1,7 @@
 version: '2'
 services:
   minigrid:
-    image: selcolumbia/minigrid-server:0.1.8
+    image: selcolumbia/minigrid-server:0.1.9
     command: ./prod/run.sh --db_host=db --redis_url=redis://redis:6379/0 --minigrid-website-url=https://www.example.com
     depends_on:
       - redis
diff --git a/prod/install.sh b/prod/install.sh
index 7eb0909..e2f8442 100755
--- a/prod/install.sh
+++ b/prod/install.sh
@@ -1,5 +1,5 @@
 #!/usr/bin/env sh
-# Minigrid Server installer for version 0.1.8
+# Minigrid Server installer for version 0.1.9
 set -e
 
 # Do you have docker installed?
@@ -108,8 +108,8 @@ $SUDO openssl dhparam -out /etc/letsencrypt/live/$LETSENCRYPT_DIR/dhparam.pem 20
 printf "========================================\n"
 printf " Generating configuration               \n"
 printf "========================================\n"
-$CURL -L https://raw.githubusercontent.com/SEL-Columbia/minigrid-server/0.1.8/prod/docker-compose.yml > docker-compose.yml
-$CURL -L https://raw.githubusercontent.com/SEL-Columbia/minigrid-server/0.1.8/prod/nginx.conf > nginx.conf
+$CURL -L https://raw.githubusercontent.com/SEL-Columbia/minigrid-server/0.1.9/prod/docker-compose.yml > docker-compose.yml
+$CURL -L https://raw.githubusercontent.com/SEL-Columbia/minigrid-server/0.1.9/prod/nginx.conf > nginx.conf
 
 sed -i s/www.example.com/$LETSENCRYPT_DIR/g docker-compose.yml
 sed -i s/www.example.com/$LETSENCRYPT_DIR/g nginx.conf