How to choose size:
Above CM in the colume is the insole length, must be longer 1 cm than your children feet length.
One way,For Example, if your children feet length is 14.6cm, you should choose US 9 with EUR 25 size and insole 15.6cm( US size is only a reference, we will shipped the right size according to the insole length )
Please been noted each shoes often have CM size tolerance due to all hand measurement.
For the battery, we can not make sure how long they can last , maybe from 1-10 days, battery can not been judged a problem after it used out, if you need, you can buy more battery that you needs