The voltage levels on my PC serial port, however, were standard RS-232 levels: -6.0 V for ONE bits and 6.0 V for ZERO bits. The voltage levels from J1 were standard TTL levels: 0.0 V for ZERO bits and 3.3 V for ONE bits. Miraculously, I was able to find a connector of the right size from some other electronics, and I connected it to J1. On the motherboard, there was a special serial port, J1, located near the wireless module. This battery is standard for many calculators and watches. I replaced the dead RTC battery with a new 1220 battery that I bought at a nearby pharmacy for $1.99. The motherboard did not need to be removed, so the display remained connected. I took apart the XO laptop, revealing the motherboard.
