I work in the commercial and industrial uninterruptible power supply industry. We use VRLA batteries for most of our setups. VRLA means Valve Regulated Lead Acid (sealed batteries essentially). Batteries heat up when you charge them, nature of the beast. However, there is a limit to how hot you want them to get and we use temp sensors to monitor that, as an option though.
When I test the batteries, my tester costs about $5k, and it shows an initial "fully charged" voltage under 13V I know that battery will fail the test and we replace it. If yours reads like that after being on the charger overnight, it's dead. BTW, a maintainer isn't really designed to charge a fully discharged battery, it's just to keep it charged, which is why it is referred to as a maintainer, it maintains the charge level, such as in a car being stored for the winter.
But as JB said, your battery is dead is it won't hold a charge.