This pump used 2 D-Cell batteries and is not rechargeable. 

Engel 2nd Generation 2X2 Portable Air Pump for Engel and other live bait coolers and buckets. Includes 12v DC car adapter, flexible hose and weighted air stone. Alkaline Batteries (2 x size D) are not included.  Top quality alkaline batteries last up 45 hours of continuous use.  Air flow volume is 0.8L/Min (slow speed) and 1.0 L/Min (fast speed).

IMPORTANT NOTE: Always place the aerator stone inside the net — never below it. Positioning the stone beneath the net causes the hose to kink and traps air pockets underneath, disrupting circulation. For even, consistent aeration, keep the stone inside the net at all times