1. Lithium ion shelf life.

Method:

Just record the battery voltage each day for 3 years, using a multimeter. 

Result:

Lithium-ion battery (9 V) shelf life in 3 years:

2. Lithium-ion charging characteristics.

Method:

Charging lithium-ion battery with a constant voltage and a constant current, record the voltage and curent in every 5 minutes.

Battery:

Nikon EN-EL3a battery (7.4 V, 1500 mAh):

Why do I choose 8.4 V and 0.6 A?

Because the charger from Nikon MH-18 specified 8.4 V and 0.9A:

 So I charged the battery with 8.4 V and 0.6 A (less than 0.9 A is ok, it will take longer time):

The result:

Lithium-ion battery (7.4 V) charging chart, charging with constant 8.4 V and constant 0.6 A:

Charged another lithium-ion battery (7.2 V, 1010 mAh) with constant 8.4 V and constant 0.4 A), not recorded every 5 minutes: