Shaking won't do much for them, Turn them up side down and strike them with a rubber mallet several times. Do this twice a year. Fire training technique.For those that carry dry chemical extinguishers on equipment, remember to take them and shake them around on a regular basis. This helps keep the dry chemical loose in the extinguisher. If left stationary on the equipment you use, the extinguishing agent can/will become compacted in the extinguisher and may not work if you need them. This applies for any type of equipment you carry a dry chemical extinguisher on.