Nimh vs. Lipo

[snaggle213]

I have a Blade CP heli that is run from the stock NIMH 8 cell packs. I have not used the heli in a few months and now the heli will not get more than 2 feet off the ground. After cycling the packs (I don't have a cycler I just used my peak charger and run them in the heli a number of times.) the problem is still there, I have replaced the motor with no change. Is this common with NIMH packs? Is there a way to bring these packs back to life? And one last question, since I may need new packs should I switch to lipos, I know the dangers and precautions to take when using Lipos. I am just wondering if lipos would last for a longer time than NIMH packs and are they more durable for storage? How many years of use can be expected out of a NIMH pack or a Lipo pack?

Thanks for any advice