BT Synergy 3500 3505 phone & Answering machine batteries.
Rechargeable batteries for BT Synergy 3500 and 3505 DECT cordless telephone with answering machine

• BT Synergy 3500 battery
• BT Synergy 3505 battery

A rechargeable pack of two AAA batteries for BT Synergy 3500 SMS and 3505 SMS cordless telephones, the BT Synergy is a DECT Handset with numerous features such as:
DECT
answering machine
Loud speaker
last number redial
caller id
Number calling display
Free speech function
Hands free operation
and many others.

This twin battery pack Fits the Following BT Synergy cordless phones
BT Synergy 3500 and 3505 DECT cordless phone with answering machine.

The Replacement BT synergy 3500 and 3505 batteries are Nickel Metal Hydride, NI-MH, they are 1.2-volts and have a storage rating of 800 Milliamps.

You should ensure you charge your new batteries for upto 16 hours, please note it may take a few charge cycles before you get full capacity.