A:Answer Hello Bruce, thank you for your question. The old battery and new battery volts must match (example 3.6V must replace with 3.6V), the battery packet size must match, and the connector must match (If you don’t know the connector size, and you have the Manufacturer and model of the phone you can possibly determine with the following website http://www.zbattery.com/Batteries/Cordless-Phone
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