Batteries are widely used in a variety of devices and because they are so common, people may not be aware of some dangers they may be exposed to when handling certain types of batteries. Two immediate dangers are:

1. fire or explosion due to a short circuit or improper charging and
2. leakage of corrosive liquid.

Other dangers include the release of toxic materials into the environment if not disposed of properly.

Kinds of Batteries:
Batteries may be grouped into dry cells and wet cells based on whether they contain a moist solid or are liquid or gel filled. They may also be divided into primary and secondary depending on whether they may be recharged.

Fire and explosion:
A battery has two (or more) terminals to deliver power to the device and if these terminals become connected (shorted out) via a material with low resistance (e.g. a piece of metal) then a very large current can flow between the terminals and a lot of heat is generated within the battery. A short may also occur inside the battery due to manufacturing defects or physical damage to the cell. In both cases (external or internal short), the battery can get very hot and may catch fire and explode.
Even small batteries can contain a lot of energy and if this is released quickly due to a short circuit, a lot of heat may be produced which generates gas that may include hydrogen (highly flammable). For example, a 3.6-volt mobile phone battery rated at 1 Amp-hour (Ah) contains 12,960 Joules of energy. A capacitor (electronic component) holding 10 joules can blow a hole through aluminum foil and a 30 Joule discharge can weld a wire to ball bearing. A 3.6 volt Lithium ion automotive cell rated at 200 Ah contains 2,592,000 Joules which is a huge amount of power.

A 9-volt alkaline battery can generate about 9 Amps of current if the terminals are connected together and the battery temperature can rise 60 to 94C within about 7 minutes [NASA Public Lessons Learned series]. A lithium ion battery that shorts out may reach 120C (Safety first -- Why all lithium batteries are not the same).

Car batteries are designed to deliver a lot of current (hundreds of amps) quickly for starting the motor. A note in Popular Mechanics magazine in March 2007 [Car Battery Do's a Don'ts] describes how a person working on a car battery touched the positive terminal with a wrench he was holding. The short circuit welded a ring on his finger to the battery hold down clamp and to the wrench. If you are removing a car battery, always remove the negative terminal first before touching the clamp on the positive terminal. This is because the negative terminal on most North American vehicles is connected to the engine and frame so touching the positive terminal to any metal on the car will allow current to flow. If you remove the connection between the negative terminal and the car metal, you have eliminated a huge area where a short circuit can occur. When installing a battery, connect the positive terminal first, and the negative terminal last.

• 2007 Feb JFK International airport - battery fire in a carry-on passenger bag
• 2006 May - fire in airplane on the ground from a spare Li ion battery in a computer bag.
• 2004 April, Chicago- fire in passenger bag before being loaded onto the aircraft. Bag contained a cordless drill with a NiCd battery and the drill overheated when it got turned on.
• 2003 Logan Airport - over heated battery found in a toolbox. It is believed that batteries terminals shorted out on metal tools.
• CR123A lithium batteries have been involved in several fires. These are 3-3.6 volt small cylindrical batteries used in cameras and several have ignited fires or exploded spontaneously or when dropped. Some incidents involve poorly manufactured counterfeit batteries coming from countries in Asia.

Check out some photos and video clips of events at airports Battery Fires in Air Transportation (PDF)

Closer to home, in October 2007, a fire occurred in the back of a University truck returning from a field site. The fire appeared to have started in a bag/box of various batteries and was likely caused by a 9-volt alkaline battery shorting out on some piece of metal or another battery. The fire burned up research notes, personal clothing, equipment and might have been much worse if the propane tanks (one full, three empty) had become involved.
Here is what the mass of batteries looked like when it was over (click on each for a larger image, press the browser back button to return here).

1	2	3
4	5	6

Battery terminals should be taped and cells immobilized by strapping together as in image 6.

Other Do's and Don'ts:
Isolate and dispose of any batteries that are physically damaged or show signs of swelling or smelling "funny".
Dispose of any battery that is punctured, deformed or that might be damaged
Remove and dispose of any battery that gets excessively warm while recharging.
Never charge a battery that is frozen. Warm to room temperature first.

Jump starting a vehicle battery:
Potential hazards associated with this procedure include shorting out the battery terminals, an explosion of hydrogen gas released from the battery and ignited, exposure to shrapnel and sulfuric acid release if battery blows up and damage to vehicle electronic components.
There is a procedure described here [Battery Safety & Jump Starting] for jump-starting a vehicle with the steps listed in sequence. Although it does not specify the disconnect procedure in step 7, simply undo the connections in the reverse sequence (i.e. 4, 3, 2, 1). The sequence is designed to avoid making sparks near the battery terminals when flammable hydrogen gas may be present.

Charging other batteries:
Follow the manufacturers recommendations and be sure that you have the correct charger for the battery. Primary cells are not designed for recharging and they may explode if you try to charge them.

Battery Disposal and Recycling:

There are some very toxic/corrosive materials in some batteries that should be prevented from being released into a landfill or water system. Large amounts of lead and sulfuric acid occur in automotive batteries and toxic elements like cadmium and mercury occur in NiCd and some button style batteries. Although there are not any very toxic substances in alkaline, lithium or carbon-Zinc batteries, it would seem prudent to avoid disposing of these into regular garbage. Environment Canada has some information about batteries and recycling. The University of Alberta collects batteries for disposal through its waste chemical disposal system (Chematix) and the City of Edmonton accepts batteries from households at its Eco-Station waste recycling depots.
At the Rechargeable Battery Recycling Corporation (RBRC) website, you can locate outlets that accept rechargeble batteries for recycling.
More information on how toxic metals are recovered during battery recycling is available at the Battery University website].