code: function (startTime, endTime, options, callback) {
      var self = this;
  
      if (typeof options === 'function') {
        callback = options;
        options = {};
      }
  
      var requestOpts = {
        path: urlJoin(_urlPrefix, 'billable'),
        qs: {
          startTime: typeof startTime === 'Date' ? startTime.toISOString() : startTime,
          endTime: typeof endTime === 'Date' ? endTime.toISOString() : endTime
        }
      };
  
      requestOpts.qs = _.extend(requestOpts.qs, _.pick(options, ['offset', 'limit']));
  
      self._request(requestOpts, function (err, body, res) {
        return callback(err, body.loadBalancers.map(function (loadBalancer) {
          return new lb.LoadBalancer(self, loadBalancer);
        }), res);
      });
    }
docs: client.getBillableLoadBalancers
  
  @description gets the billable load balancer within the query limits provided
  
  @param {Date|String}     startTime     the start time for the query
  @param {Date|String}     endTime       the end time for the query
  @param {object}          [options]
  @param {object}          [options.limit]
  @param {object}          [options.offset]
  @param {function}        callback