Included in my Ryobi printed instructions are the statements: 1-"Green LED on indicates battery pack is fully charged and charger is in maintenance charge mode. 2-"To obtain the longest possible battery life, we suggest the following: Remove the battery pack from the charger once it is fully charged and ready for use." So! "Maintenance charge mode" is not good for a battery???? My battery packs are Model P100. My charger is Model P110.

How long have you left battery on charger? It will take about 3 1/2 hrs to fully charge. t is probably not a good idea to leave the battery in the charger for long periods of time though, so once it is fully charged put it back in the drill. When fully charged the green led will turn solid. This link will have more info on charger and battery.
http://powertool.manualsonline.com/manuals/mfg/ryobi/130155001.html?p=2 C

the trimmers switch may be faulty.

CHARGING THE BATTERY PACK
Battery packs for this tool are shipped in a low charge condition
to prevent possible problems. Therefore, you should
charge them until the green LED on the front of the charger
comes on.
NOTE: Batteries will not reach full charge the first time they
are charged. Allow several cycles (operation followed by
recharging) for them to become fully charged.
CHARGING A COOL BATTERY PACK
See Figure 3.
If battery pack is within normal temperature range, the red
LED on charger will come on.
NOTE: If the charger does not charge the battery pack
under normal circumstances, return both the battery pack and
charger to your nearest Ryobi Authorized Service Center for
electrical check.
n Charge the battery pack only with the charger provided.
n Make sure the power supply is normal household
voltage, 120 volts, 60 Hz, AC only.
n Connect the charger to the power supply.
n Place the battery pack in the charger aligning raised rib
on the battery pack with the groove in the charger.
n Press down on the battery pack to be sure contacts on
the battery pack engage properly with contacts in the
charger.
n Normally the red LED on charger will come on. This
indicates the charger is in fast charging mode.
n Red LED should remain on for approximately 1 hour
then the green LED will come on. Green LED on
indicates battery pack is fully charged and charger is
in maintenance charge mode.
NOTE: The green LED will remain on until the
battery pack is removed from the charger or charger is
disconnected from the power supply.
n If both yellow and green LEDs come on, this indicates
a deeply discharged or defective battery pack.
Allow the battery pack to remain in the charger for 15
to 30 minutes. When the battery pack reaches normal
voltage range, the red LED should come on. If the
red LED does not come on after 30 minutes, this may
indicate a defective battery pack and should be
replaced.
n After normal usage, a minimum of 1 hour of charging time
is required to fully recharge battery pack.
n The battery pack will become slightly warm to the
touch while charging. This is normal and does not
indicate a problem.
n Do not place the charger and battery pack in an area of
extreme heat or cold. They will work best at normal room
temperature.
NOTE: The charger and battery pack should be placed
in a location where the temperature is more than 50°F
but less than 100°F.
n When batteries become fully charged, unplug the
charger from power supply and remove the battery
pack.
Source(s):http://toolboyworld.com/eBay/Ryobi_P110/...

get the new charger; and consider returning to store or manufacturer.
if you have the black charger, throw it out
you need the green/two-tone charger for ryobi one 18v

The Ryobi charger will flash green as it charges and then remain steady or slowly flashing green when fully charged. Flashing red means testing and if it remains steady or slowly flashing red it is defective.

Hi,

The yellow light means that there still is an amount of charge on the battery, meaning that it isn't fully discharged. The red light means that it is partly discharged and you can charge it up.

Hope this helps. If it does, I'd appreciate a 4 thumbs up. Thanks,

Handie Andie

Here is the manual:
http://toolboyworld.com/eBay/Ryobi_P120/P120_566_eng.pdf

Red = quick charge
yellow = evaluating
green = charged

CHARGING A COOL BATTERY PACK
If battery pack is within normal temperature range, the red LED on charger will come on.

Red LED should remain on for approximately 1 hour then the green LED will come on. Green LED on indicates battery pack is fully charged and charger is in maintenance charge mode.

It sounds like your battery is bad.

If both yellow and green LEDs come on, this indicates
a deeply discharged or defective battery pack.
Allow the battery pack to remain in the charger for 15
to 30 minutes. When the battery pack reaches normal
voltage range, the red LED should come on. If the
red LED does not come on after 30 minutes, this may
indicate a defective battery pack and should be
replaced.
n After normal usage, a minimum of 1 hour of charging time
is required to fully recharge battery pack.

If both yellow and green LEDs come on, this indicates
a deeply discharged or defective battery pack.
Allow the battery pack to remain in the charger for 15
to 30 minutes. When the battery pack reaches normal
voltage range, the red LED should come on. If the
red LED does not come on after 30 minutes, this may
indicate a defective battery pack and should be
replaced.
n After normal usage, a minimum of 1 hour of charging time
is required to fully recharge battery pack.

If both yellow and green LEDs come on, this indicates
a deeply discharged or defective battery pack.
Allow the battery pack to remain in the charger for 15
to 30 minutes. When the battery pack reaches normal
voltage range, the red LED should come on. If the
red LED does not come on after 30 minutes, this may
indicate a defective battery pack and should be
replaced.
After normal usage, a minimum of 1 hour of charging time
is required to fully recharge battery pack.

If both yellow and green LEDs come on, this indicates
a deeply discharged or defective battery pack.
Allow the battery pack to remain in the charger for 15
to 30 minutes. When the battery pack reaches normal
voltage range, the red LED should come on. If the
red LED does not come on after 30 minutes, this may
indicate a defective battery pack and should be
replaced.
n After normal usage, a minimum of 1 hour of charging time
is required to fully recharge battery pack.