I don't have an A4000T, but doesn't it take a lithium coin battery for the RTC? If so, just pop into radio shack and buy a coin battery holder and a 2032 3.3V coin battery. It's a simple solder job to the connections on the motherboard, just get the polarity (+/-) correct and you should be good to go. These coin batteries should last a couple of years and if you put in one of the battery holders, replacement is as simple as popping a new one in.
