Dead battery!

[Al Skierkiewicz]

Guys,
The gell cell batteries we use can be totally discharged without damage under normal loads. A dead short is not a normal load. In the event the battery we are discussing came in contact with the frame quickly, there is likely nothing more than a scrape where the contact took place. Arcing and burn marks are indications of high resistance contacts for low voltage DC. A completely discharged battery will take several hours to recharge even using the 6 amp charger.
Don't discount the possibility that the battery sustained mechanical damage when used in a robot that ran into a wall. You are dealing with a device that has a lot of mass, and that mass is concentrated in defined areas within the case. Lead is not nearly as strong as steel and a fracture in any connective structure (internal connections and plates) will result in battery failure.
The batteries are available from a variety of sources, including battery stores, McMaster and Digikey. Be sure that you order is the ES or EX type battery.
Most multimeters only can display and measure 10 amps or less and are internally fused for protection. The popular Fluke meters have two internal fuses, one for 300 mA and one for 10 Amp. To measure current on the robot, you need a current probe. Fluke makes a few nice ones but they are almost as expensive as the meter itself. They clamp on to wires under test. Remember that they can only measure current on one wire at a time. If you measure both the positive and negative leads of a motor at the same time with a clamp on probe, there will be no current measured.