Honda TRX420FPA Owner's Manual page 177

Battery
Battery Charging
Refer to Saf ety Precautions on page 95 .
(1)
(1) charger
Be sure to read the information that came with your battery charger and
follow the instructions on the battery. Improper charging may damage
the battery.
We recommend using a charger ( ) designed specifically for your 1
Honda, which can be purchased from your Honda dealer. These units
can be left connected for long periods without risking damage to the
battery. However, do not intentionally leave the charger connected
longer than the time period recommended in the charger's instructions.
Avoid using an automotive-type battery charger. An automotive charger
can overheat an ATV battery and cause premature damage.
168 Servicing Your Honda