My husband's first cell phone was Nokia 5110 about 9 years ago so I fairly know about this Nokia BLS-4 Cell Phone Battery as it was the battery pack of Nokia 5110. It uses Lithium Ion technology and a rechargeable one. It provides long talk time and keeps the cell phone powered for 4 to 5 days without recharging when purely SMS is being used. This battery is very durable as it survived countless drops on the floor when my husband used it. It doesn't bloat easily. The packaging of Nokia BLS-4 Cell Phone Battery is unique from other batteries. It is a battery pack and a back cover of Nokia 5110 in one. It is a bit bulky but is very lightweight. To remove it from the cell phone, just a light press of the upper button and a little downward pushing are needed. This is the most durable battery pack that I know of as it can be used for two to three years. It can keep the phone conversation for hours without battery-related interruptions. Nokia BLS-4 Cell Phone Battery is a great battery pack for Nokia 5110. This battery is really good.