Hach sension1 Instruction Manual page 20

SECTION 2,
continued
Figure 5 Battery Replacement
When battery replacement is necessary, replace all four batteries.
The position of the batteries in the instrument is important. Icons
of the correct orientation are molded into the bottom of the
battery compartment.
With the connectors pointing away from you, insert a battery in
left-most position so the positive end faces you. Insert the other
three batteries so the positive and negative ends alternate
(i.e, +, -, +, -). Insertion is easiest if the battery is pushed against
the spring connector first, then pressed into place.
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