On Battery Recovery Effect in Wireless Sensor Nodes

Abstract

With the perennial demand for longer runtime of battery-powered Wireless Sensor Nodes (WSNs), several techniques have been proposed to increase the battery runtime. One such class of techniques exploiting the battery recovery effect phenomenon claims that performing an intermittent discharge instead of a continuous discharge will increase the usable battery capacity. Several works in the areas of embedded systems and wireless sensor networks have assumed the existence of this recovery effect and proposed different power management techniques in the form of power supply architectures (multiple battery setup) and communication protocols (burst mode transmission) in order to exploit it. However, until now, a systematic experimental evaluation of the recovery effect has not been performed with real battery cells, using high-accuracy battery testers to confirm the existence of this recovery phenomenon. In this article, a systematic evaluation procedure is developed to verify the existence of this battery recovery effect. Using our evaluation procedure, we investigated Alkaline, Nickel-Metal Hydride (NiMH), and Lithium-Ion (Li-Ion) battery chemistries, which are commonly used as power supplies for Wireless Sensor Node (WSN) applications. Our experimental results do not show any evidence of the aforementioned recovery effect in these battery chemistries. In particular, our results show a significant deviation from the stochastic battery models, which were used by many power management techniques. Therefore, the existing power management approaches that rely on this recovery effect do not hold in practice. Instead of a battery recovery effect, our experimental results show the existence of the rate capacity effect , which is the reduction of usable battery capacity with higher discharge power, to be the dominant electrochemical phenomenon that should be considered for maximizing the runtime of WSN applications. We outline power management techniques that minimize the rate capacity effect in order to obtain a higher energy output from the battery.

Sensitive magnetometry reveals inhomogeneities in charge storage and weak transient internal currents in Li-ion cells

“…As is documented in the literature, long-term continuous discharging of the battery followed by a disconnection of the terminals leads to a "recovery effect," where the battery voltage relaxes to a higher equilibrium voltage level over a period of time (22,23). The magnetic sensors recorded transient fields that we associate with this voltage increase based upon the well-matched long-term time constants of the exponential relaxation to a steady-state value.…”

Scheduling of dual supercapacitor for longer battery lifetime in safety‐critical embedded systems with power gating

“…Shin et al in [9] presented a new B‐SC system having a constant‐current charger which isolates the battery from SC to improve the end‐to‐end efficiency for energy from the battery to the load while accounting for the C‐rate of lithium (Li)‐ion batteries and the conversion efficiencies of the converters. In [10], Narayanaswamy et al proved the non‐existence of charge recovery effect in batteries through their detailed experimental evaluations. They identified that the C‐rate as the dominant electrochemical phenomenon which can be minimised to obtain higher‐energy output from the battery through both hardware‐ and software‐based power management approaches.…”

Experimental validation of the recovery effect in batteries for wearable sensors and healthcare devices discovering the existence of hidden time constants

“…Another set of studies which have been carried out with the aim of analysing their ability to show recovery effect have been previously described [4, 10]. Narayanaswamy et al [4] placed alkaline, Ni–metal hydride (MH) and Li‐ion batteries under constant power discharge for 0.5, 5 and 50 s followed by a rest time for the same period. The battery voltage, power and energy were analysed.…”

“…Therefore, to analyse the performance of batteries in realistic situations, the sleep current should be taken into consideration. Furthermore, as previously stated by Narayanaswamy et al [4] the intermittent discharge profile of the battery should be compared with the continuous discharge which has the same average power of that of the intermittent discharge. It is claimed that this is a fair comparison between the two profiles instead of comparing the peak power continuous discharge with the intermittent.…”

“…These experiments were conducted on specific chemistries and size of the batteries, and hence do not generalise to a battery of every size and shape. In contrast to the literature reporting the benefits and utilisation of recovery effect, it has been recently stated that recovery effect is just an illusion and has been wrongly used in all the literature stating its benefit [4]. It has been suggested that the parameters used for identifying and measuring the recovery effect are inappropriate.…”