Chassis battery.. Likely is dead
House battery: If MARINE/deep cycle there is slight hope it will recover
If GC-2 pairs a fair chance it will recover.
This is why I keep telling folks that DEEP CYCLE batteries (GC-2 pairs) should be kept at least half full
MARINE/deep cycle (Most Group XX) 3/4 full
Starting batteries (Chassis) 80 or more
And in all cases recharged quickly when run down.
And people argue with me.. but you just proved it.
NOW.
When plugged in measure voltage AT THE BATTERIES.. should be over 13 and a half.
But if it's not.. You have a charging issue.. Converter, Fuse (Or circuit breaker), Disconnect switch (In reverse order of suspect)
NOTE circuit breaker can be a 120 volt (likely labeled conv) or 12 volt.