This dehumidifier from Hydrosorbent comes with an inbuilt recharge indicator. The indicator is initially orange in coloration, but it really turns by itself very clear when it demands a reactivation. This humidity is drained out or gathered in an inner tank when the dryer air is launched to the area. https://dstdehumidifiers.co.uk/case-studies/desiccant-dehumidifiers-in-cold-stores/