We have BT Studio 1100 with three handsets. From working well, they all became dead. We have changed the batteries. The phone line is working, and there is electricity reaching all the cradles which light up when a handset is placed on them.

it is too far away from the base and battery is dead

Pull the battery for 5 minutes

Check and replace the battery.

is possble to use 8 bt 6500 hand phones via 2 base unit on the one bt line

press hold power button for 5 sec and reset and re pair the device

I had the same problem with KX-TCD220E and BT line. Cured by changing the DSL filter.

Help
My Bt Studio 3100 cordless telephone ( 2 Pack ). I have carried out the setting up procedures as per instructions.
Handset batteries are fully charged, but I am not getting the dialling tone.

To Mrs Sue Groom,
You probably need to register the handsets to the base.This is the user manual for the BT Studio 1500
http://www.shop.bt.com/content/uni2/documentation/43py/023626.pdf

I have found this free link on BT site for you
http://www.shop.bt.com/content/uni2/documentation/498n/025455.pdf

If the second handset works ok on the base and the first handset doesn't, then you are right...the fault lies with the first handset. There are batteries ( special type ) in the handset, it sound as if either the batteries are dead, or not charged ( try charging them for 12 hours on the good base station ) or the connection is bad.