It is about the same size as the keyboard and touchpad of a 17 inch laptop and is powered by 4 AAA batteries. The batteries do last for quite some time but you can save yourself a small fortune by getting some alkaline rechargeable batteries. Note, these are not the same type of rechargeables that you by at your local supermarket as they are only 1.3v and only last 2 weeks at best. These alkaline rechargeable batteries last about the same length of time as standard batteries but can be recharged and so used again and again.
The keyboard itself is compact and the touchpad is located just under the spacebar key. This gives enough room to rest your hands either side of the touchpad when typing. This is useful if you are not using the keyboard at a desk and have it on your lap. There are 2 retractable feet so if you do have a desk you can angle the keyboard for easier typing.
The keys themselves are well made and respond well without having to press too hard. I find that the letters on the keys tend to fade quickly on many of the cheaper keyboards but the white lettering is just as clear today. I have found that the matt coating on the keys does erode over time making them shiny especially on the spacebar as it is used a lot. The colouring on the casing itself also fades after a while where I have been resting my hands. That being said it doesn't impede the ACK 540RF keyboards performance. One quibble I do have is the lack of a range of other colours for the casing as many people want to match their keyboard to their computer colour.
Other than that this is a great budget wireless keyboard with built in touchpad (with scrollbar facility) that really lasts well. The lack of a battery power light makes it frustrating when the batteries do go as you are not sure if it is your computer that has gone haywire. The only way I know the batteries are about to fail is the mouse pointer starting to jump.