Testing battery state of health with portable metering devices?

The state of health of a battery is not easy to assess without testing the discharge. Besides, what is of more interest for France Telecom is remaining autonomy at constant power load. Several solutions are proposed using permanent test or monitoring systems or portable test devices. Without discussing the methods of measurements and their results, France Telecom R&D has evaluated the functional aspects of three portable testers based on the impedance or the conductance measurement for a possible use in the maintenance of the batteries. The tests have shown several critical points in the use of these devices. Thus, the point of measurement on a battery block is important: the resulted value is not the same whether the measurement is carried out on the terminals of the battery, the screws or the bars of connections. In addition, choosing a reference for a model of block is not obvious, because measurements of different sets of new batteries from a same manufacturing batch have shown an important dispersion, which involve a personalized follow-up of each block, leading to a huge number of data to manage. This personalized follow-up also involves that the configuration of the batteries strings of the site should not evolve with time, with the risk of modifying new measurements and thus to distort the history and the detection of bad health battery. The testers have failed in identifying youth defaults of new blocks revealed on the France Telecom R&D batteries testing bench. Lastly, the duration of measurements can be important according to the sites configuration and the accessibility to the battery terminals. This study has shown that the use of this type of testers is constraining in terms of time, of capacity and data management. The conclusion of these tests trend France Telecom to a monitoring using permanent system.