[word=batteries] □ □ □
[word=batteries] [□] □ □
[word=batteries] (□ | □) □ □
The robot runs on batteries , navigates around most obstacles and can handle most lawn shapes . All necessary electronic circuitry , including batteries , is located inside the housing . The unit is only slightly bigger than an iPod , operates on two AA batteries , offers microphone and guitar inputs , and features built-in drum tracks . The power switchboard used for handling all heavy currents required in the exchange , such as the currents for the charging and ringing machines , and the charging and discharging circuits of the storage batteries , is located next to the wall of the storage-battery room . One from home , the student brings with tape and batteries , puts on teacher 's desk , and takes back home again .