It is normal for the battery to read 12.8V or more when fully charged. As a matter of fact, if you can't get 12V, the battery is finished it's useful life....
Below is copy from the 2007 service manual (available from this site)
Ciao,
Maverick
▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼
a. Connect a pocket tester to the battery terminals.
NOTE:
• The charge state of an MF battery can be
checked by measuring its open-circuit voltage
(i.e., the voltage when the positive battery
terminal is disconnected).
• No charging is necessary when the open-circuit
voltage equals or exceeds 12.8 V.
b. Check the charge of the battery, as shown
in the charts and the following example.
▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲
5. Charge:
• Battery
(refer to the appropriate charging method
illustration)
WARNING
EWA13300
Do not quick charge a battery.
CAUTION:
ECA13670
• Never remove the MF battery sealing
caps.
• Do not use a high-rate battery charger
since it forces a high-amperage current
into the battery quickly and can cause
battery overheating and battery plate
damage.
• If it is impossible to regulate the charging
current on the battery charger, be careful
not to overcharge the battery.
• When charging a battery, be sure to
remove it from the vehicle. (If charging
has to be done with the battery mounted
on the vehicle, disconnect the negative
battery lead from the battery terminal.)
• To reduce the chance of sparks, do not
plug in the battery charger until the battery
charger leads are connected to the
battery.
• Before removing the battery charger lead
clips from the battery terminals, be sure
to turn off the battery charger.
• Make sure the battery charger lead clips
are in full contact with the battery terminal
and that they are not shorted. A corroded
battery charger lead clip may
generate heat in the contact area and a
weak clip spring may cause sparks.
• If the battery becomes hot to the touch at
any time during the charging process,
disconnect the battery charger and let the
battery cool before reconnecting it. Hot
batteries can explode!
• As shown in the following illustration, the
open-circuit voltage of an MF battery stabilizes
about 30 minutes after charging
has been completed. Therefore, wait 30
minutes after charging is completed
before measuring the open-circuit voltage.
▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼
Charging method using a variable-current
(voltage) charger
a. Measure the open-circuit voltage prior to
charging.
• Positive tester probe →
positive battery terminal
• Negative tester probe →
negative battery terminal
Example
Open-circuit voltage = 12.0 V
Charging time = 6.5 hours
Charge of the battery = 20–30%
NOTE:
Voltage should be measured 30 minutes after
the machine is stopped.
b. Connect a charged and AMP meter to the
battery and start charging.
NOTE:
Set the charging voltage at 16–17 V. If the setting
is lower, charging will be insufficient. If too
high, the battery will be over-charged.
c. Make sure that the current is higher than
the standard charging current written on
the battery.
NOTE:
If the current is lower than the standard charging
current written on the battery, set the
charging voltage adjust dial at 20–24 V and
monitor the amperage for 3–5 minutes to
check the battery.
d. Adjust the voltage so that the current is at
the standard charging level.
e. Set the time according to the charging time
suitable for the open-circuit voltage.
Refer to “Battery condition checking steps”.
f. If charging requires more than 5 hours, it is
advisable to check the charging current
after a lapse of 5 hours. If there is any
change in the amperage, readjust the voltage
to obtain the standard charging current.
g. Measure the battery open-circuit voltage
after leaving the battery unused for more
than 30 minutes.
▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲
▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼
Charging method using a constant voltage
charger
a. Measure the open-circuit voltage prior to
charging.
NOTE:
Voltage should be measured 30 minutes after
the machine is stopped.
b. Connect a charger and AMP meter to the
battery and start charging.
c. Make sure that the current is higher than
the standard charging current written on
the battery.
NOTE:
If the current is lower than the standard charging
current written on the battery, This type of
battery charger cannot charge the MF battery.
A variable voltage charger is recommended.
d. Charge the battery until the battery’s charging
voltage is 15 V.
NOTE:
Set the charging time at 20 hours (maximum).
e. Measure the battery open-circuit voltage
after leaving the battery unused for more
than 30 minutes.
▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲
6. Install:
• Battery
7. Connect:
• Battery leads
(to the battery terminals)
CAUTION:
ECA13630
First, connect the positive battery lead “1”,
and then the negative battery lead “2”.
8. Check:
• Battery terminals
Dirt → Clean with a wire brush.
Loose connection → Connect properly.
• Reach the standard charging current
Battery is good.
• Does not reach the standard charging current
Replace the battery.
12.8 V or more --- Charging is complete.
12.7 V or less --- Recharging is required.
Under 12.0 V --- Replace the battery.
12.8 V or more --- Charging is complete.
12.7 V or less --- Recharging is required.
Under 12.0 V --- Replace the battery.
