In my experience, only with Canon DSLR so far, when properly used and disposed, DSLR batteries can last for very long time without failing.

For example, I'm still using a couple of batteries I bought about 8 years ago with a Canon 550, and I'm still able to shoot at least 300 pics before they run out of juice (when they were new I could shot at least 400 shots). Since lithium battery technology is similar, I expect also Nikon batteries to last for so much time.

So if a battery is not faulty from the start (it's uncommon, but can happen), I expect it to last for quite a long time.

As far as I know, there are a few things you can do to make batteries last longer:

• Use them. If you have 3 batteries, use mark them with a number, and use them in sequence, so you know you're using all of them.
• Recharge them after each use, and before use. I usually recharge my batteries the day before and the day after any photo shoot.
• Try to avoid extremely hot of cold temperature. Don't leave them in your car trunk in a sunny day, and put them in your pocket when you go on a snowy hike.
• Don't let them fully discharge. They will last longer, and you won't miss the moment for a special shot.

One last thing - batteries may be faulty, and with some experience you may find out strange behaviours quite soon. Ask for replacement.

In Europe law gives you 2 years of warranty on almost any product, and I guess it wouldn't be too different in other countries. Get in touch with the store that sold you the battery, or with the manufacturer.