The upgrade 7 cell battery has the same little black connector as the stock 6 cell battery that came with your Slow-V. If you need another adapter for the charger, call Horizon Hobby and order one from them.

Try not to get frustrated waiting for good flying weather. You might want to consider getting up early and flying right at sunrise. In most areas that is when the wind is at its least. There have been many days here when there has been virtually no wind at 6:00AM, but too much wind to fly by 8:00AM.