). This analysis revealed that the increases in 2,6-DHAQ crossover rate during constant-current charge were exacerbated at higher currents (Figure ), supporting the conclusion that this effect is driven by migration of 2,6-DHAQ ions. Though we note that there is some cellto-cell variability, the magnitude of this effect is significant relative to the calculated errors (see Methods S9). Importantly, unlike the predictions from previous theoretical studies, the increase in crossover is significant; migration appears to double the rate of crossover during the 50 mA constant-current charge. This shows that battery operation has a non-negligible impact on crossover, even at low currents. Optimisation of the charging protocols could also be considered as a route to mitigating crossover. When choosing the optimal charging current, there is a trade-off to consider between crossover rate and the time period per charge. The time taken for a 10 mA charge is approximately five times longer a 50 mA charge. So, although crossover rates are lowest when a low current is used, the time period over which crossover rates are elevated is longer. To determine which charging current is optimal for mitigating crossover, the total amount of 2,6-DHAQ crossover was calculated for each charging period (Figure , Methods S9). Here the background (i.e. diffusional) crossover is assumed to be constant, and is estimated from the average background crossover measured at the start of the experiment before battery charging. When the total amount to crossover is compared to the background crossover during one charge period, it appears that the crossover enhancement increases with decreasing current. Therefore, over the current range examined, the highest current was found to be optimal for mitigating 2,6-DHAQ crossover during a constantcurrent charge.