You may not pack spare lithium batteries in your checked baggage.
You may pack spare lithium batteries in your carry-on baggage.

If you pack a device containing batteries, secure it against activation by locking the activation
switch to the “off” position, placing the device in a protective case, or by appropriate measures.
For personal use, there is generally no restriction on the number of spare batteries allowed in
carry-on baggage. This is the case for cell phone batteries, “hearing aid” button cells, and AA
batteries/AAA batteries available in retail stores, as well as almost all standard laptop computer
batteries.

• Keep batteries and equipment with you, or in carry-on baggage – not in your checked
  baggage. In the cabin, the cabin crew can better monitor conditions, and have access to the
  batteries or device if a fire does occur.
• Buy batteries from reputable sources and only use batteries approved for your device – avoid
  counterfeits. A counterfeit battery is more likely to cause a fire in your equipment – costing you
  more in the long run, and compromising safety.
• Look for the mark of an independent testing or standards organization, such as Underwriters
  Laboratories (UL) or International Electrotechnical Commission (IEC).
• Do not carry recalled or damaged batteries on aircraft. Check battery recall information at the
  manufacturer’s website, or at the Consumer Product Safety Commission.
• If original packaging is not available for spare batteries, effectively insulate battery terminals
  by isolating the batteries from contact with other batteries and metal. Do not permit a loose
  battery to come in contact with metal objects, such as coins, keys, or jewelry.
• Place each battery in its own protective case, plastic bag, or package, or place tape across
  the battery’s contacts to isolate terminals. Isolating terminals prevents short-circuiting.
• Take steps to prevent crushing, puncturing, or putting a high degree of pressure on the battery,
  as this can cause and internal short-circuit, resulting in overheating.
• If you must carry a battery-powered device in any baggage, package it to prevent inadvertent
  activation. For instance, you should pack a cordless power tool in a protective case, with a
  trigger lock engaged. If there is an on-off switch or a safety switch, tape it in the “off” position.