Does anyone know if the batteries continuously hold 80% or more charge over extended periods of disuse?

Or is it like NiMH and NiCad where the batteries discharge over a few weeks until there's practically no power left in the cells?

Edit:

Got this from Amazon's review page on the batteries and charger:

Upon closer examination, many of the alleged benefits of NiZn turn out to be just marketing hypes. For examples:

"Higher Energy Density":
Despite what the confusing rating on the package ("2500mWh") may suggest, the PowerGenix AA cell does NOT contain more energy than a SANYO eneloop AA cell. This is because its current capacity is much lower at just 1500mAh (based on data sheet of PowerGenix AA cell, and verified by my own testing).
- Energy in eneloop AA cell: 1.25V * 2000mAh = 2500mWh
- Energy in PowerGenix AA cell: 1.65V * 1500mAh = 2475mWh

As an example: Suppose a set of 4 eneloop AA cells can power your external flash unit for 1500 shots, then a set of 4 PowerGenix AA cells will provide roughly the same number of shots. The difference is that your flash unit will recycle about 30% faster with the NiZn cells due to 30% higher battery voltage. On the other hand, this high rate of fire could cause the flash to over-heat and burn out.

"Long Cycle Life":
PowerGenix claims that NiZn has a service life that 'meets or beats' that of NiMH cells. But according to technical data found on PowerGenix web site, the NiZn cell is only rated for 200 cycles at 100% deep discharge. Most NiMH cells are rated for 500-1000 deep discharge cycles.

"Long Shelf Life":
PowerGenix claims the NiZn cells have longer shelf life than Lead-Acid batteries (which are notorious for high self-discharge rate), but did not compare against NiMH cells. In the "Charging Procedure" section, it says to recharge the NiZn battery every 30 days!


In summary: While the higher voltage offered by PowerGenix NiZn cells sounds attractive, it could damage or shorten the life span of your battery-operated appliances. In addition, NiZn cell does not pack more energy than eneloop NiMH cell, yet it suffers from lower cycle life and higher self-discharge rate. So unless you are desperately looking for higher voltage rechargeable batteries, there are really no reasons to take your chances with those cells.

So in all, 80% marketing hype, 20% usefulness. 200 deep discharge cycles is pathetic.