It is similar to the shelf life measurement used for primary batteries. The time at which a battery is considered depleted and should be recharged or discarded. Each of these chemistries has distinct advantages and disadvantages. NiCad NiCad has been used in defibrillators for years. It was used in early cellular telephones and still finds uses in rechargeable power tools.
NiCads are particularly unsuited to AEDs for several reasons.
They have a high self-discharge rate and will become discharged in less than 3 months. They require very high maintenance, which involves periodic discharging of the battery and then recharging. SLA SLA batteries were the initial choice for portable AEDs. It is well understood technology that requires only moderate maintenance, and is very reliable if kept fully charged at all times. SLA batteries have moderate shelf life staying fully charged for six months.