// /override/classes/Product.php
<?php
Class Product extends ProductCore
{
    public $quota;
    public $initial_quota_value;

    public function __construct($id_product = null, $full = false, $id_lang = null, $id_shop = null, Context $context = null)
    {
        self::$definition['fields']['quota'] = array('type' => self::TYPE_INT, 'validate' => 'isInt', 'size' => 2);
        self::$definition['fields']['initial_quota_value'] = array('type' => self::TYPE_INT, 'validate' => 'isInt', 'size' => 12);
        parent::__construct($id_product, $full, $id_lang, $id_shop, $context);
    }
}
?>


/adminxxxx/themes/default/template/controllers/products/prices.tpl

<div class="form-group">
    <div class="col-lg-1"><span class="pull-right">Cantidad de cuotas</span></div>
    <label class="control-label col-lg-2" for="quota">
        <span class="label-tooltip" data-toggle="tooltip" title="Cantidad de cuotas"></span>
    </label>
    <div class="input-group col-lg-2">
        <span class="input-group-addon">#</span>
        <input maxlength="2" name="quota" id="quota" type="number" value="{$product->quota}" />
    </div>
</div>
<div class="form-group">
    <div class="col-lg-1"><span class="pull-right">Valor cuota inicial</span></div>
    <label class="control-label col-lg-2" for="initial_quota_value">
        <span class="label-tooltip" data-toggle="tooltip" title="Valor cuota inicial"></span>
    </label>
    <div class="input-group col-lg-2">
        <span class="input-group-addon">$</span>
        <input maxlength="12" name="initial_quota_value" id="initial_quota_value" type="number" value="{$product->initial_quota_value}" />
    </div>
</div>