Hello and thank you for your question. That message simply indicates that you need to replace the batteries in the keyboard. The A500 uses four AA batteries with the battery compartment located on the back panel.
If replacing the batteries does not solve the issue then there may be some type of a hardware problem, but that is not likely.
I just wanted to add that If you are powering it via USB, the Lo message may be indicative of the computer not providing enough power. This commonly occurs with laptops, especially when they are running off of the battery. It can also occur when the computer only supports older USB standards, or if a non-powered USB hub is in use. Placing a powered USB hub between the computer and the keyboard should remedy those types of problems.