Zoom H4n Pro Operation Manual page 17

When a "Low Battery!" warning appears, immediately
an AC adapter.
If the remaining battery
charge
"Low Battery" will be
shown every two sec-
onds and the unit will
FULL
EMPTY
becomes low,
You can use conventional alkaline and nickel metal hydride
rechargeable batteries.
Connect a USB cable that is already connected to the
USB bus power and the unit will turn on automatically. This
function is only available when the H4n Pro is used as an SD
card reader or an audio interface.
The remaining battery charge can be measured more
precisely by using the H4n Pro battery type setting.
If the batteries die or the power supply is interrupted, the
H4n Pro will retain the date and time setting for about three
minutes. After this, these settings will be reset to their default
values.
Using batteries Using AC adapter
P.033
USB bus power
P.130
Battery type
016