IBM 560 - Manual (Page 21)

Battery Pack
The ThinkPad computer uses a lithium-ion (Li-Ion) battery pack that
meets the following electrical specifications:
Figure 1-10. Battery Pack Specifications
Nominal Voltage + 10.8 V dc
Capacity (average) 2.2 ampere hours (AH)
Protection Overcurrent protection
Overvoltage protection
Overdischarge protection
Thermal protection
ThinkPad 560/560E System Overview 1-13