Magento – Magento2 custom attribute default value

         /**
         * @var $th Mage_Eav_Model_Entity_Setup
         */
        $th =new Mage_Eav_Model_Entity_Setup('core_setup');
        $th->addAttribute(Mage_Catalog_Model_Product::ENTITY, 'credit', array(
            'group'                      => 'Prices',
            'type'                       => 'text',
            'backend'                    => '',
            'frontend'                   => '',
            'label'                      => 'Credit rewards',
            'input'                      => 'text',
            'global'                     => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_GLOBAL,
            'visible'                    => true,
            'required'                   => false,
            'user_defined'               => true,
            'default'                    => 'kkkkkkkk', // this is default value.
            'searchable'                 => false,
            'filterable'                 => true,
            'comparable'                 => false,
            'visible_on_front'           => true,
            'visible_in_advanced_search' => true,
            'used_in_product_listing'    => true,
            'unique'                     => false,
            'apply_to'                   => 'simple',
        ));

Try to set default value as string

'default' => '0'

or empty

'default' => ''

Update

The default values are added when you add new product for old ones it not affects.

Try to fix that in Product management with mass action

Inside manage products, there is a action called “Update Attributes”. Select all the products that you want to update and then select Update Attributes and add all the new information in.