Honda 2012 TRX420TM Owner's Manual page 177

Battery
Battery Charging
Refer to Saf ety Precautions on page 89 .
(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 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.
Servicing Your Honda 169