I asked the same question in July. The following is the reply I received.
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Thank you for your recent e-mail.

The 7C can use the following batteries:

FUTM1457 NT8S600B TX NICD 600MAH 6DA/8U for $44.99
HCAM6362 NIMH 9.6V 1650 SQ TX U SANYO for $54.99

Any prices provided are Manufacturers Suggested Retail Pricing only. As a distributor, we support our dealers by selling directly to them. Typically your favorite Great Planes authorized hobby shop or mail order firm like Tower Hobbies ( http://www.towerhobbies.com/ ) is able to provide you with better pricing and excellent customer service.

To locate a dealer/hobby shop/retailer here in the US, please visit our web site and click on the "dealer locator" tab to locate a retailer or distributor near you. If you are in the US, click on the highlighted "retailer" and enter your zip code. This will provide you a list of dealers in your area. If you are an international customer, please click on the "international distributor" tab on our web site and you will be able to locate the international distributor nearest to you.

Sincerely,
John G.- PS9004
Product Support Lead Technician
Futaba Programming Technician
Great Planes Model Distributors
www.futabarc.com