Graco Duet Connect Owner's Manual page 26

For Safe Battery Use
not replaced or recharged at the same time. Do not mix old and
Any battery may leak battery acid or explode if disposed of in fire
or an attempt is made to charge a battery not intended to be
for a cell of another type.
Discard leaky batteries immediately. Leaky batteries can cause skin
burns or other personal injury. When discarding batteries, be sure to
dispose of them in the proper manner, according to your state and
local regulations.
month or more. Batteries left in the unit may leak and cause damage.
product ceases to operate satisfactorily.
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