## 3 Results  
The results from the cycling tests--_hard AK3.4_ and _soft AK3.4_--are presented. The loss of residual capacity after cycling \(C_{loss}\) is the difference between the measured capacity at the beginning and the residual capacity \(C_{res}\) measured during aging tests. The decay of \(C_{res}\) over the full cycles equivalent (\(FCE\)) for all four test cells (\(TC\)) are presented in Figure 4. Additionally, the cell voltages measured at the end of the 5 h pauses after cycling and recharging are shown in the second graph of this figure. These open-circuit voltages (\(OCV\)) presented here are still superimposed by over-potentials, as the duration for the voltage to relax after charging or discharging required longer pauses for lead-acid batteries [24].  
From the beginning of the aging test until 90 FCE, \(TC1\) and \(TC2\) of _hard AK3.4_ and \(TC2\) of _soft AK3.4_ had similar rates of capacity decay. Toward the end of the aging test, the capacity of \(TC1\) in the _hard AK3.4_ test decreased faster and ended at 0.94 Ah after 135 FCE, while the last capacity of \(TC2\) in the _hard AK3.4_ test was at 2.84 Ah after 150 FCE. In both cases, the test was interrupted after the discharge voltage dropped below 1 V during cycling. \(TC1\) in the _soft AK3.4_ test lost its capacity with the fastest rate. After 90 FCE, the residual capacity was 0.82 Ah, which is also when the voltage dropped below 1 V. It seems that \(TC1\) in _soft AK3.4_ was not correctly reassembled, but results from this test cell are presented and discussed here. The aging test on \(TC2\) in _soft AK3.4_ is still ongoing.  
The SoC during the _hard AK3.4_ cycling test was not set periodicaly with a full charge of the test cells. Therefore, the SoC during the check-up can only be assumed with the observation of the OCV  
Figure 4: The upper figure shows the residual capacity \(C_{res}\) of the test cells in _hard AK3.4_ and _soft AK3.4_ aging tests over FCE. The capacities were measured after cycling with a discharge current of \(-41_{20}\) until 1.8 V. The lower figure shows the OCV after cycling phase (blue) and after recharging (red) of the test cells over FCE.  
right before the impedance measurement after cycling and after recharging. In Figure 4, the OCV values differ between the test cells, which is caused by differences in acid concentration. The measured OCV values after recharging are higher than after cycling. This is caused by over-potentials from the charging phase rather than an increased SoC. Charging over-potentials can remain from hours to days in a lead-acid battery. This behavior has been analyzed by [PERSON] et al. [24]. The OCV values measured after cycling might be superimposed by over-potentials as well. The OCV values of _soft AK3.4_ measured after cycling, compared with those of the _hard AK3.4_ test, indicate either a higher SoC or higher over-potentials. In _hard AK3.4_, the values decrease by at least 2 mV and at most 15 mV from the beginning to the end of the aging tests. This indicates an SoC drop during the test. It can be assumed that the decrease in measured \(C_{res}\) is provoked not only by sulfation but also by the SoC decrease. In the test cells, the OCV changes only by 0.25 mV with an SoC change of 1%. Based on the measured OCV values and the OCV SoC relationship, the SoC of \(TC2\) in _hard AK3.4_ would decrease by 60%, and the \(TC1\) in _hard AK3.4_ would decrease by 25%. These SoC changes are assumptions, as a correct SoC estimation using OCV would require significantly longer rest phases until the measured voltage no longer over-potentials [24].  
During the _soft AK3.4_ test, the test cells were frequently recharged for 24 h, so that after charging the SoC could be set. The OCV values during _soft AK3.4_ varied, but they did not decrease continuously.