Hypercycle is a technique to use a rechargeable NiMH battery to extend it's life cycle and maximize overall usage.

Example:

10% Depth of Discharge x 300,000 cycles = 3,000,000 overall percentages

60% Depth of Discharge x 10,000 cycles = 600,000 overall percentages

The difference is 5 times more in overall usage.

The short answer is to use it a little at a time. 

As the graph above shows, you would get about 700 cycles if you use 100% at a time. This means you charge it fully and draining it until empty. Isn't it how you use those rechargeable AA NiMH batteries?  Yes, the worst possible way and now you know. If you discharge it at 60%, NiMH would be good for 10,000 cycles! That's more than 27 years if you use one cycle every single day! This gets better with 50% depth of discharge as it would double the cycles to 20,000. A little dirty secret NiMH battery charger and rechargeable battery manufactures don't want you to know.

Prius normally uses less than 10% at a time. It is also known as one hypercycle. Prius HV battery is used when the gas engine is inefficient and therefore unlike an electric vehicle, no more than 10% is usually used at a time. This understanding enables NiMH to last 300,000 cycles! Toyota has warranty for 10 years or 150,000 miles on the pack. This means, Toyota believes an owner will average 2 HV cycles per miles. If an owner averages 1 HV cycle per mile, the HV battery pack would last 300,000 miles! If an owner drives mostly highway and use only 0.5 HV cycle per mile, it should last 600,000 miles!

See below excellent graphs from Wayne Brown's site:

Knowing the abusive behavior is the first step in preventing it. If you are a Prius owner you may not be aware of your abusive actions to the Prius. Toyota designed the Prius so the computer does not allow abuse. However, there are trade-offs that had to made between fuel economy and battery life. You can avoid extensive use of these features to hypercycle your HV battery and still get excellent MPGs.

It is 100 deg F outside and you are stuck on a long traffic jam on the highway (ahem, parking lot). You have the A/C on and crawling with gas engine off. The battery would drain to the pink levels in about 5-10 minutes until the gas engine would kick in to recharge it. I am sure this has happened to you before. Ouch! You have just used about 40% depth of discharge!

To minimize it, set the climate control to 78 or 80 deg F. Point the air vent toward your face and body. If possible, close the passenger vents to maximize cool air directly toward you.

During the jam there may be a stop and go pattern between 5-15 MPH. The gas engine may not start when accelerating at that low speed. You can avoid acceleration with battery by sudden accelerator movement to force the gas engine to run. You can then let it go slightly and HV battery will be recharged while the car is accelerating. This trade-off (use of gasoline) is better for the long traffic jams since you are preserving precious battery power for lighter use.

If you have a modded EV button and use the HV battery until the pink bars, don't! Now you know the reason why Toyota USA disabled the EV mode in the Iconic Prius (2004-2009) model. 2010 Prius comes with factory EV button but more restrictions were implemented to prolong the HV battery pack life.