New Driver First Car

I've owned my 2008 Prius for only 10 months. Granted it is almost 10 years old, I've never had a problem with it and I've racked about 15,000 miles on it for a grand total of almost 160,000 miles. So here's my issue. Last weekend my boyfriend and I were driving back from Indiana and going up a hill when the check engine light started flashing on the dash and the car started jerking. We were both alarmed but I thought it was just low on oil. As soon as we get to the top of the hill the car is fine again and the check engine light is gone; added some oil just to be sure. Just a quart no big deal. We sit for a minute and let it run then continue on our journey home. No issues car isn't acting strange at all. Then we got on the highway and started up another hill and the check engine light is flashing or stays on, then this red triangle with an exclamation mark comes on and my battery is completely drained. A cop sees us struggling and helps us out, and he said that motors fan should be on (I couldn't see it) but the alternator was running just fine. I told him about how the info part of the prius's options and have him look at it. Unfortunately he's not very familiar with cars and doesn't know what it means. Being that the engine is EXTREMELY hot he tells us to give it a break and try to recharge the engine after letting it cool for a bit. We did so and it worked fine and went up the rest of the hill at only 45mph with the cop supervising us from behind so we weren't endangering anyone (he was so so kind) finally got the battery charged and went home the car jerking a little but not nearly as harsh. Now it's been a few days and I've been checking the engine frequently but the fan in the front of the car doesn't seem to be working. Does it only turn on while driving? The triangle went away after that night after a day of rest, and the check engine light turned off last night. Is there any suggestions out there? Does my battery need replaced or is it just the fan? Do I need another oil change too?