Siemens Tek Battery

Hello I have a set of Siemens Nitro aids with a Siemens Tek Connect and the battery is going out in the Tek and was wondering if there is another brand of battery that will work? I look up Siemens 3.7 V 1000mAh 3.7 watt and find all kinds of batteries that look similar, has anyone had to get a new battery, from where and what brand and model number?
Thank you for your time and response.