NEC VERSA TXI Manual page 4

Turn the system around so battery latches are facing you.
5.
Each latch is made up of two sliders. See the following figure.
6.
Rectangular slider (labeled '1' on the system).
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Bullet-shaped slider (labeled '2' on the system).
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Both sliders must be locked for the latch to secure the battery.
Each latch requires a two-step action to lock the battery in place.
7.
Move the rectangular slider toward the center of the latch (A in the following figure).
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Move the bullet-shaped slider toward the center of the latch (B in the following figure).
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4 NEC Versa TXi 15-Cell Maximum-Life Battery
Locating latches on the Maximum-Life Battery
A – Two Latches
Latch sliders both unlocked