Days in Inventory. The formula to calculate days in inventory is the number of days in the period divided by the inventory turnover ratio. This formula is used to determine how quickly a company is converting their inventory into sales.
How long do hearing aid batteries typically last? A standard hearing aid battery lasts anywhere from 3 to 22 days, depending on the hearing aid type, battery type and capacity, and the amount of hearing aid use. How do I know if I should change batteries? Change your batteries if sounds become distorted or you have to turn up the volume more than usual.
1 Your devices are more than three years old. Hearing aids typically last for three to five years. If your hearing aids are beyond three years old, repair needs are likely to pile up, in which case it makes more financial sense to get some new devices.  The damage is visible.