They are all pretty much the same. Look for one that uses a D size battery so it lasts longer. Some also come with an adapter so they can be plugged into the cigarette lighter in a car.
Use a multi-coloured plastic airstone or no airstone. Don't use normal sand airstones because they put too much back pressure on the pump and the battery goes flat sooner or they don't pump much air.
Put a lead weight (plant anchor) on the end of the airline to hold it down.
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You can buy a power inverter from an auto store and they plug into the cigarette lighter of a car. The other end of the power inverter is a normal power point/ socket. You can plug a normal air pump into the power inverter and use it while travelling in the car, then use the battery pump to keep air going into the bucket/s when you are out of the car.
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Have the car's air-conditioner on to stop the water temperature getting too hot in the car.