Regal 3300 Owner's Manual page 121

The battery hardware features a red boot to protect the positive terminal
and a battery tray with hold-downs. Make sure the red (positive) boot
is completely covering the positive terminal of the battery. Check the
terminal nuts periodically for tightness and corrosion.
RED OR "+"
BOOT
In colder climates consider battery removal for the winter months.
Trickle-charge as needed, placing battery on wood in a well-ventilated
area free from any gas or propane appliances.
Never charge a battery in the boat or directly on cement. Remove
the battery from the boat first. Check the water level periodically on
non-maintenance-free batteries. Add distilled water only.
Contact your closest Regal dealer for further battery information and
service schedules.
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Systems
4-9