Yes, you can bring AA batteries on a plane. According to TSA regulations, dry batteries such as C, D, AAA, and AA are allowed to be packed in both carry-on and checked luggage.
Quantity limits: None for most batteries — but batteries must be for use by the passenger. Batteries carried for further sale or distribution (vendor samples, etc.) are prohibited. There is a limit of two spare batteries per person for the larger lithium ion batteries described above (101–160 watt hours per battery).
Lithium metal (non-rechargeable) batteries are limited to 2 grams of lithium per battery. Lithium ion (rechargeable) batteries are limited to a rating of 100 watt hours (Wh) per battery. These limits allow for nearly all types of lithium batteries used by the average person in their electronic devices.
Damaged, defective or recalled lithium batteries must not be carried in carry-on or checked baggage if they are likely to be a safety concern by overheating or catching on fire. When in doubt, leave it out. Check the FAA's Pack Safe website for the rules on carrying these items and other dangerous goods in baggage.
Firearms, ammunition, and fireworks are prohibited, as are all knives and safety razors (including pocket knives and Swiss Army knives). Straight razors and replacement blades for straight razors are also not allowed. Most tools also cannot be packed in carry-on luggage, as they have the potential to cause harm.
Good news! Most are allowed in carry-on or checked bags depending on the type of product and if they are battery operated. Battery operated toys that use traditional non-rechargeable batteries (AA, AAA, etc.)can go in checked or carry-on bags.
Safety Razors: Because the razor blades are so easy to remove, safety razors are not permitted in your carry-on luggage with the blade. They're fine to pack in your carry-on without the blade. The blades must be stored in your checked luggage. The same applies for straight razors.
A flashlight that is less than 7 inches in length and is not classified as a tactical weapon can be brought on a plane through carry-on. You can bring any flashlight through checked luggage but you must carry lithium batteries with you in your carry-on bag.
Batteries are picked up very vividly by baggage scanner machines used in the airport security process. These scans are diligently assessed by security. This is why laptops are required to be removed from carry-on luggage before the screening unless you have TSA Pre-Check.
What can happen if I accidentally forgot some portable electronics that use lithium batteries in my check in bag? Generally nothing happens. You can carry most electronic devices with installed lithium batteries in checked luggage. You cannot carry loose batteries or ones in external chargers.
This covers typical dry cell batteries and lithium metal and lithium ion batteries for consumer electronics (AA, AAA, C, D, button cell, camera batteries, laptop batteries, etc.) Spare (uninstalled) lithium metal and lithium ion batteries are always prohibited in checked baggage and must be placed in carry-on.
Toothpaste is considered a liquid by the TSA (Transport Security Agency), even though it's technically a paste. In fact, all pastes, gels, waxes, and lotions are also classified as liquids. And even today, these substances are still restricted by the 3-1-1 rule in hand luggage due to safety threats.