Sounds more like a shorted cell, if the battery was dead, wouldn't get anything. Back in the good old days, a 6V battery had three cells, connected in series, been this way for over a hundred years now, each fully charged cell should show 2.15V at 25*C. If one is bad, like shorted out, instead of reading 6.45 V across three cells, would only read 4.3 volts.
Back then, only had to replace the bad cell, with a 12 V battery, and to save on manufacturing cost, get rid of those extra straps, solder them internally, so instead of reading 12.9 volts would only read 10.75 volts. But you can't replace that one bad cell, have to replace the entire battery.
Your car is a computer and with this lower voltage, do not get sufficient voltage to run all these electronics, and in particular a Power On Reset, microcontrollers are so confused, start reading code someplace up the stream then generate all kinds of weird codes.
Voltage drops with even a good battery can also cause these kinds of problems. Corroded connectors, loose terminals, and even dirty relay contacts.
Really all you need to troubleshoot these problems is a voltmeter.
In a 12 volt battery with six cells, each has to be perfectly balanced, because they are all charged and discharged in series. Each cell consists of many plates in parallel, if one plate is not soldered correctly, its capacity will be lower, and it will overcharged boiling off the electrolyte and then shorting out with exposed plates. This could be corrected if you had individual caps where you can check the level of the electrolyte to prolong the life of the battery.
But you can't do this with a maintenance free battery, no caps.
So calling these maintenance free batteries is not exactly correct, a far more appropriate name would be a throwaway battery.
These are all over one hundred year old facts. Ha, the Prius battery has something like 200 cells in series, one takes one cell to go bad to destroy the entire mess. But great for selling new batteries, depends on which side of the fence you are on.