I'm sorry you got suckered into thinking this was a good purchase. Used hybrids are rarely a better option than a small four-banger.

Possibilities:

1) The seller likely knew the battery was marginal and didn't disclose
2) Low mileage hybrids aren't great. The fact that the car sat a lot is actually hard on the batteries too.
3) Odometer was a lie. It actually has much higher mileage and a hacked-together battery that wouldn't last any longer than was necessary to get it sold.

Drive the car to the nearest O'Reilly Auto Parts (No, not Autozone or anybody else, O'REILLY ONLY!). Have them read the CODES (a 5 digit alpha-numeric code). MAKE SURE YOU GET THE CODES. DON'T LET THEM INTERPRET OR GIVE YOU THE DESCRIPTION. GET. THE. CODES.

Your location and the car's history would be helpful as well.

 

This is absolutely not the car a college student with limited funds should own.

The previous post asked where you are in part because if you are in a state which requires smog tests you are in more trouble than otherwise. If the IMA light is on it also lights the CEL, and a car will not pass smog (at least in California) like that. Bypassing the IMA is probably considered an illegal emissions modification in that state too. You care because if it cannot pass the smog test it cannot be (re)registered, and then you cannot legally drive it.

If the IMA battery isn't too far gone you can keep it limping along for a while, maybe a year or so, by periodic grid charging. The equipment to do so isn't that expensive, but you have to know what you are doing, have a place where you can do it, and have time for it. If you go this route be sure to change the CVT fluid frequently, lest the equally expensive transmission go out.

Economically the most logical thing you could do would be to sell the car, even at a loss, and buy a conventional economy car. A reliable IMA replacement battery will cost you around $3K if you do all the work yourself. If (when) the CVT goes that would be another $3-4K. Spending that is nuts when you can buy a conventional 2004 Civic for around $2K. Yes things will break there too, but they will usually cost less to fix. Even if the transmission goes it will be something that many shops can work on - nobody fixes CVTs, and all the replacements are refurbs of unknown quality.