seen in fig9 the inner wall 109 has a ledge 112 which extends from the first part 105 the ledge 112 is the second electrode of the charging cap 102 and is arranged with a second spring element 113 so that the ledge 112 is spring loaded against the rechargeable unit 103 when inserted into the charging cap 102 at the inner wall 109 at an edge part 114 of the wall 104 two clamping members 115 are attached the clamping members 115 are in the present example arranged to extend from an outer surface 116 of the wall 104 through the wall 104 and extend far enough off the inner side 109 in order to be able to engage in corresponding recesses 115 a on the rechargeable unit 103 when the rechargeable unit 103 is inserted into the charging cap 102 the charging cap 102 is further provided with a female socket 117 to receive a cable for connecting with for example but not by way of limitation an ac dc adapter 118 the rechargeable unit 103 comprises an end surface 119 having a centered on off button which is arranged to function as a third electrode 120 the end surface is encircled by a fourth electrode 122 in the present and preferred example the fourth electrode 122 raises above the end surface 119 but embodiments wherein the fourth electrode is in level with.