A couple of thoughts,
- You did nothing wrong by removing the battery. You saw a potential issue and took action to prevent it. In the conditions you described unnecessary
but you solved your concern. I wish a few select co workers thought that way until further advised.
A benefit of all this is if you've never removed the battery on your own before, now you know you can. And you got to see the condition of the cable, the work of others, saw anything you would like to change, ect. This was not a waste of time if you've learned some things about your battery set up.
- I realize it's the holiday and you were looking for advice but, when working on a battery only ask the battery manufacture
in this case Deka. The world is swimming with incorrect info about batteries. Battery manufactures are highly motivated to have us users be successful with their products.
- OK, it's not impossible for a lead acid battery to freeze but
it will need to be discharged and really cold. Here is the tech sheet for a Lifeline AGM. I realize you have a Deka and these temperature vs State of Charge will vary a bit among brands. However, of the high quality brands they will perform close enough to the Lifeline. The exception is my battery which is a UPG made of Chinesium which performance is less than the big names. So I baby it more.
Page 23 is where Temperature tables can be found.
The key here is keeping your battery state of charge and thus the electrolyte above where it will be damaged. It's pretty forgiving if your always above say 75 % charged. At that SOC it would have to be so cold it would exceed the antifreeze in your motor. The usual scenarios of failure are, batteries were stored discharged all ready then went to -10F, batteries were all ready bad and self discharged over the winter and froze, a small load like a CO detector was discharging all winter while at -10 and froze. SOC is the key to storing and using batteries in cold. And you solved that by plugging in a maintainer.
Hope this helps