Add this code to your featured-product.liquid template after product is defined.
After this code
{% assign product = ... %}
Add this code
{% if product != empty %}
<script>
sizeChartsRelentless.product = {{product | json}};
{% if product.collections %}
sizeChartsRelentless.productCollections = {{product.collections | json}};
{% endif %}
{% if all_products[product.handle].metafields.sizechartsrelentless.size_charts %}
sizeChartsRelentless.metafield = {{all_products[product.handle].metafields.sizechartsrelentless.size_charts}};
{% endif %}
</script>
{% endif %}