Connect multiple 3.7 V Lithium-ion Polymer Battery in parallel
Once connected, it's safe to charge and discharge a pair of permanently paralleled cells as if it's a single cell of their combined capacity.

However, the process of connecting them must only be done when they have the same terminal voltage. A large and dangerous current will flow if you connect two cells of significantly different charge state. A good technique is to initially connect them with a resistor for a while to let them self balance at a safe current.