Newly developed nickel-metal hydride (Ni/MH) micro cells that are capable of high rates, meet the requirements of main power sources for modem wireless telecommunication devices, like GSM hand phones, PDAs and others. Besides having the capability to give high continuous and pulse discharge currents, they also ensure the realisation of a device with slim design and low cost. For the back-up of the RTC function, a lithium-ion cell based on the carbon-manganese dioxide system provides high reliability by having a long cycle life and complete tolerance to deep discharge. For MBU (which require higher rates), a Ni/MH cell only 2 mm thick is now being introduced. Other wireless devices, like headsets for comfortable use of mobiles whilst driving, wireless mice and keyboards and the upcoming "Bluetooth" technology will need suitable power sources. Besides the rather high currents, which exclude low-power lithium systems, miniaturisation is limiting the space available for the: battery. Some concepts using Ni/MH micro butteries will be discussed in this paper.