Okay. Bay trees in containers. Possible reasons for brown and leaf drop include:

Overwatering/too much soil moisture:
Have you repotted recently?   They should only be transplanted into a pot that is slightly larger than the old one. They won't tolerate wet feet. Drainage is important so add some stones to the base of the pot before adding compost when repotting, put some feet under the pot to raised it off of the ground. If pots are in a tray that holds water remove the tray.   Too much water can also cause the bark to split.
Underwatering when in storage/indoors can also have delayed effects when placed outdoors but that doesn't sound like it is your problem. Watering should be done sparingly- when soil is dry to the touch.
Over/Under fertilization- What is your feeding regimen? Too much especially non-organic (other than fish,bone, blood meals) can burn the plant roots and cause leaf drop.The damaged roots can be more susceptible then to over watering.
Wind and cold damage can also cause leaves to brown and drop off. At temperatures below freezing, you will have damage. We grow them here and overwinter them in the outdoors- in the ground. Often they die back to the ground, but every spring the old leaves do die and turn brown and fall off when new ones are growing out.

Finally, you could have insect or disease problems here. Insect problems that are common on Bay include woolly aphid that feed by piercing/sucking on leaf, stem and trunk tissue, leaf cutter bees, vine weevils that eat the edges of leaves

Another insect is called a bay sucker- Lauritrioza alacris - whose feeding causes mostly young leaves to thicken, curl inwards, and become malformed. The leaves sometimes curl up and if you unroll them you can sometimes find the insect inside.

Disease problems of bay leaves include Shot hole fungus that should be best treated via prevention- increased air circulation, avoid overcrowding, encourage vigorous growth.  If your plant also has black sooty looking coating on stems or leaves, it is caused by aphids or scale insects feeding on the plant. You can wash away this sooty mold with water with a little bit of soap in it. Spray it on and wipe each leaf and stem off carefully. If there are insects present you will see them generally on the bottom of leaves and in the crevices of leaf/stem connections. If they come back you may need to treat with an insecticide preferably a systemic one that is delivered via root drench.

If there are no insects or insect damage present, the cause of the brown leaves is almost certainly environmental - too much or too little water possibly, damage from cold and wind or occasionally too much heat. The key to coping with this damage is to get the conditions correct for your bay tree. Follow the steps below and then wait and see what happens over the next six months, chances are that your tree will recover:

So what to do? Maintain and optimize the health of your plants:  
Remove brown and dying leaves. Do not remove leaves with less than 30% damage as they can still do some beneficial work for the plant. Inspect them for signs of insect damage/presence. Dispose of them away from your compost pile.
Examine your watering program to ensure adequate, regular soil moisture without excessive moisture retention. Make sure that water will drain freely from containers.
Replace soil with new compost that is worked into the roots after removing some of the old soil. Fertilize using a small amount of low nitrogen source of potassium and phosphorus, preferably organic low-analysis organic source. This could be mixed into the new compost.  
Do a soil analysis to ensure that you are maintaining the preferred pH of the soil as well.
I note that the Royal Horticulture Society has a publication on Bay tree cultivation that might be useful too.

Good luck!