NEC 750C - Manual (Page 26)

Getting Familiar with Your MobilePro 750C 2-13
NOTE
If you receive messages indicating that both
the main battery and the sub-battery (back-up bat-
tery) are very low, replace the back-up battery first.
If a drained main battery is not replaced, the back-
up battery drains more quickly than normal.
2. Disconnect any cables attached to the unit, such as the
AC adapter cable.
3. Have a new back-up battery available.
! WARNING
Only replace the back-up battery with a CR2032
Lithium battery.
Using another battery type can result in an explo-
sion or fire.