>a) when using a battery grip do both batteries work at the same time >or one at a time?
When using Nikon Grips, specifically the MB-D200, MB-D100, and the MB-D80 (the only three Grips that use Dual Batteries in the grip) the batteries are used one at a time. First one battery is used, and when depleated the second battery is used.
>(b) is the voltage on the non branded batteries and issue?,
There have been issues with many third party batteries over the years. Some have good luck with them, others nothing but problems. The third party batteries, I tried several years ago in my D200 would not even allow the camera to power up when turned on. The Nikon batteries I replaced them with have continued to work perfectly to this day. That was about 6 years ago.
>(c) should I maybe look into other replacement batteries, if so any >recommendations(looking to maybe get something more affordable >than stock nikon)?,
Personally I would recommend getting a Nikon battery and not looking back.
>(d) did they die out so fast because they where stored too long >without being used?
While all batteries lose power when not used for long periods of time, getting only 80 shots on two batteries seems very low for sitting for only two months. I have had batteries stored for a lot longer than two months and they held about 90% of their charge.
>Another question, since I have 3 batteries and only have one >charger, stock, any recommendations on a dual battery charger?
The Nikon MH-22 (D3 Series) and the MH-26 (D4 Series) both priced north of $300.00 have duel slots but only charge one battery at a time. Charging three batteries sequencially on after the other on your charger shouldn't be that much of a problem. If you really feel the need, get another Nikon MH-23 Charger. Good Luck and Enjoy your Nikons!