My battery maker (TQ) gives the following criteria:
Only use this product within following temperature limits
Operation: -5 °C to 40 °C / 23 °F to 104 °F
Charging: 0 °C to 40 °C / 32 °F to 104 °F
Storage: 0 °C to 40 °C / 32 °F to 104 °F
Recommended storage: 10 °C to 20 °C / 50 °F to 68 °F
Have ridden it at or near the stated max operating temp and I'm certain the summer sun heats the office bike locker well above that, but as the battery is not removeable, there it is.
Rest of the time the bike resides in the garage, with the charger.