diff --git a/app/models/cost.rb b/app/models/cost.rb
index 6909ebd..cc70b2d 100644
--- a/app/models/cost.rb
+++ b/app/models/cost.rb
@@ -161,7 +161,7 @@ class Cost
         # charge battery with return_kwh
         return_kwh -= battery.charge(return_kwh)
         
-        if low_hour.eql?(formatted_hour)
+        if lowest_hour.eql?(formatted_hour)
           # charge battery during lowest hour
           usage_kwh += battery.charge(max_charge_kwh)
         else