Couple of things:

1) If you signed a paper when you took it in to him, authorizing him to do the work, then you have to pay him or he'll put a lien on you.

2) $120 isn't bad, to pay someone else. A $30 battery probably wouldn't meet the amperage requirements of your car, unless you drive some ridiculously small piece of shit (what do you drive?), and wouldn't last very long.

Next time, get an estimate only. Problem is, not many mechanics will give a free estimate, and rightly so.

Either way, before you go to the Better Business Bureau, talk to him about it, give him a chance to make you leave happy. If he is unwilling to do so, then get the BBB on his ass.

Don't resort to childish bullshit. If he knows you're pissed, and shit starts happening, you will get a visit from the local constabulary. Guaranteed. Even if they can't prove you did it, it's good to stay under the radar.


One final piece of advise, to all of you:
If you don't know shit about cars, don't buy a car that will need to be worked on. You'll spend just as much paying someone else to fix it as you would have to buy a good car.