These are AA rechargeable Batteries.  The batteries are NiMH, which do not have memory issues when charging.  They are also 2500mAHr, which is much more powerful than most rechargeable batteries you can get in stores.  The Trekker requires 8 batteries, these will save you money over time.

Note, the picture of the battery may not be represenative of what we have in stock at any given time.  We use different suppliers, etc so the batteries may have different covers, but they are all high quality AA NiMH batteries.