Lithium ion batteries are known for their high energy density but so does the Li-polymer battery that even allows a slight increase. Solid polymer is flexible which makes it possible to create batteries into various shapes and sizes including thin films. It is common to find lithium polymer batteries that are relatively thin like the one used by Nokia BP-4L in several devices. Li-polymer batteries can be made very slim like a credit card that can fit neatly into stylish mobile devices so that they can be made lighter and extremely thinner than their counterparts to attract a lot of attention in the competitive market of mobile devices.
The charge and discharge characteristics of lithium ion batteries and lithium polymer batteries are the same and do not require a special charger. Safety issues are also alike since both require protection circuits. However, gas buildup when charging a Lithium polymer battery may cause the foil packages to swell so that manufacturers need to make some allowances for expansion. Li-polymer battery in a foil package can be less durable than a lithium ion battery in a cylindrical package; however, this issue is solved by packaging the Lithium polymer battery in a cylindrical package. Similar to the lithium ion batteries, the lithium polymer batteries slowly degrade from the date that they have been created. If you are going to buy a new battery pack, make sure it is new and it has not been sitting for a long time on the store shelves. Both batteries also prefer partial discharges and they hate heat which can cause their degradation.