Ring doorbell keeps going offline

Removable battery ring door bell keeps going offline. We have 2 batteries and it happens when either one are in. We charge battery, reboot wi fi and re-add doorbell but it happens time and time again. No other items WiFi is dropping, it worked fine for 1st year. We thought it may have had a fault from when we had hot weather but it still keeps happening. How can I get it to work all the time 😀