You can easily measure this on device. Write code that performs what you described. Charge battery to 100% and then run the code. After a day or two connect to it to check how much battery was used. Or you may even use events to send battery status to Cloud. Now you can calculate how many percents per unit of time device is consuming and from that how long it will work till battery reaches 0%. You can use 2 devices from DevKit to average results.
LTE Beacon battery capacity is 800mAh, not 500mAh. Do you plan to use smaller battery? If so this may cause unexpected behaviour of the device and it is not supported.
You may extend battery life of the device by connecting it via USB-C to an external power source such a power adapter or battery bank.