Googling seems to suggest this is a PWM (vs MPPT) charge controller. Which are fine, just produce about 15-20% less power than MPPT.
What are you using your system for? I mean, what are you powering from the inverter?
To answer your question, yes, you can just attach to the two posts. Most batteries only have two posts, the ones you had with 4 posts are less common.
Also, a 3000W inverter on a 12v system doesn't really work very well, if at all, if you max out at 3000W. If you never run more than 1200-2000W, then no big deal. But if you try to run more than 1000W (regardless of inverter size) from a single 100Ah lithium battery, you will likely trip the battery's protection circuit and it will stop discharging. It will re-set itself in a few minutes, but you do not want to trip the charging or discharging protection circuits on a regular basis, as it could eventually damage the battery if done too many times. To get around this, you could put two or three 100Ah lithium batteries in parallel for more amps. 2x100Ah = 2100W continuous. 3x100Ah = 3200W continuous.
Or you can buy a 100Ah lithium (lifepo4) battery that has a 200A rating (can discharge at 200A continuous before the protection trips), but those are more expensive, so a 2x100Ah would double your amps (each generally has 100A rating) as well as double your capacity. And will extend the life of both of your batteries since they will share the amps (if pulling 120A, each will contribute roughly 60A), which means less heat and too much heat is what tends to kill electronics of any kind quicker than anything else.
If you ever reached close to the 3000W max of your inverter on your lead acid batteries, there's a good chance you deeply discharged them. Lead acid doesn't do well with deep discharges, but lithium handles it with ease. When lead acid are discharged deeply repeatedly, they will become permanently damaged and will no longer perform like they used to. I am SO glad to have switched to lithium...lead acid is such a headache
