I have been doing 50-90s with my various 400AH ish battery banks over the years without any real trouble until now, using the inverter to run MW, kettle, and toaster as desired.
The usual battery advice is to keep draws and charging under 25% of capacity.
MW at 125amps is 125/450 = 28%
Kettle at 90 amps is 90/450 = 20%
Toaster at 70 amps is 15.5%
The only problem in the past has been voltage drop to keep the inverter from shutting down. I typically have about a 0.8v drop from whatever the bank's voltage is at the time.
The goal is to be able to run the toaster once for three minutes in the morning of a recharge day, when at 50% SOC or 12.1 volts. That makes it drop to say 11.3, and you hope the toast is done before it sinks to 11 and sets off the inverter alarm.
So with various banks of mixed 6s and 27s, 6s and T-1275s, AGMs and 6s and T-1275s, nothing like this ever happened.
I think it is very weird that these AGMs could still do all that until recently as described in the OP. They can still do it as long as they are above 75% SOC (according to voltage being above 12.7ish)
I don't know what the bank capacity is anymore. They can do the 20 hr rate for a long time, down lower than 75% SOC. But they have no capacity at the higher rates once voltage gets to about 12.7.
Peukert went on strike! Mex explains that somehow I did damage these AGMs, but doing the same things to my previous batteries did not do anything like this. So whatever I am doing "wrong" , all I need to do probably is go back to using Wet deep cycles that can "take" whatever I am doing.
Meanwhile, I will see how far I can get by adding a couple of Wet 27DCs to this AGM bank since I have them handy. If it doesn't work, or when it stops working well enough, whatever, then it is obvious what the next step must be.
