Default [Q] How long is standby battery life?

I'm new to Photon, Just got a used one from ebay.
I was get bad battery life (~1 day with minimal use). So I turned off everything, put it in airplane mode, killed all of the running apps and wanted to see how long it can run standby. To my surprise, it's still ~1day. It doesn't seem to make any difference that it's in airplane mode with none of the stock services running. Does this seem normal?

How long should I be able to keep Photon alive in airplane mode?