Radio Shack TRS-80 PC-3 Owner's Manual page 23

(4) Replace the two batteries observing the correct
polarity. (Fig. 11)
Figure 11
(5) Replace the battery cover by sliding it in the
reverse direction of the arrow shown in figure 2.
(6) Hook the claws of the back cover into the slits
of the computer proper. (Fig. 12)
Battery cover------til---4+
Figure 12
21
~
+--+----Lithium Battery
.=_=_=_,,=_==,_0
"-",
I
I;LiJ