Update asserts for battery price

src/Entity/Battery.php

@@ -118,6 +118,8 @@ class Battery
     // selling price
     /**
      * @ORM\Column(type="decimal", precision=7, scale=2, nullable=true)
+     * @Assert\NotBlank()
+     * @Assert\Range(min=0, minMessage="This value should be a valid number.")
      */
     protected $sell_price;