I own 2 genuine vholdr batteries now for my 1080HD system. People are having problems with poor quality aftermarket batteries. The genuine vholdr runs for a tad over 3 hours - enough to fill the 16GB disk easily with room to spare.
As with any new battery, you should charge it and drain it 3 times to "wake it up" upon receipt. This, and keeping it in a charged state, will prevent premature failure.
Now to tell if you bought a genuine product - the packaging is very distinct - clear plastic box folded from thin sheet plastic and meant to be hung on a rack. The box is much larger than the battery, and includes a small instruction card. Finally, both the box and battery carry the VholdR logo. Any other cheap packaging indicates a cheap battery. I bought mine from amazon and got the real thing which works fine with their system.
Technical specs: 1050 mAH Li-Ion, with 3 terminal sensor for charging properly.
Finally I don't want to stereotype that all non-OEM accessories are sub-par but as far as batteries go for cellphones, I have a motorola that will run 4-5 days while so called "super-aftermarket" batteries can barely keep it alive 30 hours without any use. Given these are the same size batteries I'd expect the real product to be essential here. I have designed products with Li-Ion batteries and met with the companies in China who make them - they are not ashamed to inform you that statistically one in 100,000 cells will fail explosively. That's 10 parts per million fail rate. But put 10 cells in a laptop and now it's a 100 part per million fail rate on laptop batteries since they have so many cells. So far this li-ion problem has only been improved, not eliminated, so stick with products designed for your system. As for other batteries, my GM car has an interstate battery that I replaced, and my honda has the factory battery which lasted 6 years.