You've got 144V if they are 12V batteries.
If the charger only puts out 120V and your pack is 144V you've got problems. Sounds like you need to figure out the charger. As far as getting the marine chargers, depends on how fast you want to charge. And buying new batteries, I'd buy what I want for batteries. You may even find some re-furbished like I did at SMS battery. Brand new, nothing wrong, but half price.
Although, having had the cash, if I were to do it all over again, I'd have gone lithium from the start. Expensive, getting cheaper every day, but way better than FLA.
Also check into the 12V BMS, thought it was here somewhere. Simple two diodes and a light bulb. Worked great on my 144V pack.