The built-in flashguns found in compact cameras and some SLRs are inflexible and of limited power. If used frequently they soon exhaust expensive camera batteries. A flashgun that fits on a hot-shoe on top of the camera, and uses its own batteries, is more satisfactory. Non-dedicated units are effective, but dedicated models are better. They are fully integrated with the camera's electronics and may feature red-eye reduction and autofocus assist illumination. With the correct lead, they can also be used off-camera. This increases flexibility and helps to eliminate red-eye. More powerful hand-held units are also available. These use larger rechargeable batteries, have faster recycling times and must be connected to the camera using an appropriate lead.