If the battery has got very hot and the terminals/cables also , disconnect it now , as said it’s knackered and potentially a fire hazard and the fumes are harmful also .
Dont try and resurrect it it isn’t worth the risk and tbh it will be fruitless.
I would be amazed if you have x3 starter batteries though I would have thought they would be more likely domestic bank , but could be wrong .
Pop into Sutton or Boulters and they can replace it for you and also check your alternator output , hopefully is just a case of a battery wearing out .