Before you can understand how you can extend the life of your batteries you will need to know a bit about the batteries themselves. Nickel Metal Hydride batteries do not form a memory, so you can charge them as much or as little as you need at any time without damaging the ability to recharge the battery. The battery will also form crystals on the inside if left in an inert state for too long.
Charge your batteries when you first get them. It is not necessary to charge them fully. However, since they are already on the charger it will not take much time to charge them to full capacity.
Every couple of months you will need to run the batteries all the way down to zero power. Doing so will prevent the battery from forming crystals in the area that has not been discharged. This will allow the battery more charges and longer life cycle.
Do not let the NI-CD Rechargeable Battery set unused for long periods of time. They can make them crystallized as well. Another way that you can cause permanent damage to your NiMH batteries is to let them sit in a discharged state. Either store them fully charged or keep them on the charger. Most charges have a smart feature that allows the batteries to be charged when left on the charger without causing damage.
You can store charged NiMH batteries in the fridge or freezer in order to prolong the life of the battery as well. Alkaline batteries are not significantly affected by cooler temperatures. In fact, NiMH batteries can withhold ninety percent of their energy capacity when stored in a refrigerator or freezer.
Store your batteries in a plastic bag if you are putting them in the fridge or freezer. This will keep the moisture out of the 18650 batteries and prevent them from being damaged. Batteries that are cold do not allow the full voltage capacity to be reached. It is recommended that you let them settle to room temperature before using them in your electronics.
These are two methods that you can use to expand the life of your rechargeable NiMH batteries. You can use them simultaneously or separate from each other to get the best possible power from your batteries.