Mod drained batteries WAY too low

[B NEAT]

-Paranormal 250c about 2 years old plugged in over night every night 

-New-ish Molicel P26As (Aug 2019) swapped out every couple of weeks (or when I forget to plug it in at night)

-For the last year I've been  using one of those magnetic USB adapters/magnetic cord (really handy) because my USB socket started failing to connect

-I hardly ever change any settings on my Mod, including the day before this occurrence. 

One morning about a week ago I got a "check battery" warning when I got out of bed (the worst time for that to happen). I staggered downstairs and popped in another set of Molicels and continued on with my morning routine. About 10 minutes later it dawned on me that when I put the dead cells into my charger it read something like 2.4 not the normal 3.4! I ran back to my charger to double check and by then they were up 2.5 or 2.6 charging at .5A.  It's only happened that one time and the Mod and that pair of batteries seem to be fine. Can anyone explain what could've happen to cause this?

One thing I should add is that in hind sight I MAY have notice my screen lit up when I grabbed my mod that morning, but I'm not really sure. (I don't wake very quickly) 

[dwcraig1]

 Welcome.

Since it was a one time thing I would't worry about it too much but would certainly keep an eye on it

[B NEAT]

Thanx for the response, I'll definitely be keeping an eye on it. 

BTW, I remember you from ECF. Long time no see!