[New to XS Power battery]

I have a xs power hf1215 charger am I able to do it with that? I haven't charged it since I posted this just been sittin in my appartment so it can have a rest voltage and reads between 12.4 n 12.5. By the way I wanted to buy a xs power d1200 for under the hood since the d3100 didnt fit in there, also a xp3000 battery and parallel them is it possible. 

[New to XS Power battery]

I have had this battery for almost a year. I bought it used for 200 bucks was resting at 12.6v 12.7v.  I used it just for my subs since it does not fit under my hood In a 2002 Honda civic lx. 2 months ago it stayed at 12.4 and i bought a 12v xs power charger. Rright now i checked with a multi meter n it was at 11.8v I didn't turn my sub on for 2 months because I wasn't sure if my battery is bad. It will sound weird when I turned my sub on like it would bass once I turn it on then tune down not sure if my battery is bad or I just wired something wrong I have a d3100.