First of all I have a really stupid warning. If your shop has metal countertops, don't leave your charger clips laying on them
Second, I have a fiarly stupid warning. When you are charging your batteries make sure there is no way the clips can touch at all. Besides the charger shorting (maybe about 6 amps), you'll be shorting the battery at over 200 amps
In some instances all these things can weld themselves together and you wouldn't be able to stop it from shorting.
Third, this is my main warning that I started this thread about. Last week, my team was charging this old battery (02 or 03) that seemed like it just wouldn't tanke a charge because it must have been really dead. The light on the charger stayed on orange for a while, like over a day. We though maybe the charger detected the battery's deeply discharged state and decided to trickle charge it. Apparently this wasn't the case. After a few more days we found that the light was still orange and the sides of the battery were bulging out and cracked in three places.
Moral of the story: don't leave your batteries charging for too long, even if the charger says they aren't done.