That is how lithium batteries work, basically little to no warning as the voltage drops in a hurry to completely dead in a few days. Just like lithium batteries on cordless drills etc. Many camera users are used to a slow gradual voltage drop over time with alkaline batteries. Essentially, lithiums go from 100%, to 90%, to 60%, to dead over a few days. Furthermore, most trail camera battery meters cannot/do not accurately display lithium battery voltage/percent left. Get you a $20 volt meter from hardware store if you care to accurately measure lithium battery voltage to estimate how much life is in them. 1.7-1.8 volts brand new, then almost dead at 1.5 volts.