An external battery solution is for people who don’t have an outlet nearby and who don’t care that a cable and battery box are visible in the vicinity of the fountain. Having a battery outside of your water fountain or using a detached battery compartment leaves more room for water inside the fountain. You can choose between a D-cell box or using a rechargeable Li-Ion USB battery (power pack). As in all of our battery options, we do not supply the batteries but provide tips on which batteries will work. The batteries must be purchased separately from a reputable dealer. Amazon is a good choice because it’s fairly easy to exchange/return a battery that doesn’t work and since new choices are continually becoming available, we cannot test them all.