The battery charge controller chip, U1015 next to the 3-pin battery connector is TI bq24035
"Dual Input Li-Ion Charger with Dynamic Power Path" which can charge
the internal 4.2V Li-Ion battery either through external +5V in
connector, or 5V USB power applied to docking station connector pin 12.
The middle wire on the battery connector is a temperature sensor
(thermistor to ground), used to cutoff charge in case of battery
overheating. See fig.2 on p.11 of the bq24035 data sheet. I think this information should be at the z2 chip list page, but it is not.
The 14-pin chip marked AER915 just below the expansion port is a 80C51-type microcontroller, similar to Philips P89LPC915. It has an 8-bit A/D which is used to determine which of six buttons are pressed on the resistor-network wired remote. It communicates with the main cpu via I2C.
Caution: even "identical" SD cards may not be the same. Some will boot in the Z2, and some will not. See for example these two Kingston 2GB microSD cards, both purchased from Amazon.