Just to throw in a little commentary:
I've been in charge of designing a propulsion system (motor, battery, propeller) for my senior design team's airplane. Due to this (and the AIAA DBF guidelines) I've become fairly well-acquainted with how batteries run.
I'll mainly comment on a few things:
These are what I've had many many hours of experience researching down to a dot since AIAA (American Institute of Aeronautics and Astronautics) doesn't allow LiPo batteries for use yet.
1. I've heard that they don't allow as much current output as NiCD but you can get individual cells that output 50 amps continuous and over that much in bursts (only a few seconds) - for a ton of uses you probably won't pull over 50 amps anyways and definitely not paintball lol.
2. These batteries slowly discharge on a curve. What I mean by this is that over time their voltage will drop until a certain point where their resistance will become higher than their available power and the cell will "die." This is based on how quickly the current is drained.
3. Something you should really note on each battery you get is the mAh (milliampere-hour) which is supposed to be an indicator of how long your battery will last if a certain current is applied. However, as noted before, if you start pulling higher currents then this milliampere-hour rating starts becoming less and less.
4. NiMH have a higher energy density than NiCD and no memory effects (as noted on the first page) IMO if you can't -or don't want to- use a LiPo or Lithium Ion then go with these.
General batteries (non-Lithium)
1. The voltage drop is nice if you're looking for a good indicator of your battery life. If you measure your battery voltage and compare it to a fresh battery you'll roughly know how much life you have left. Another good thing to look at is your battery voltage while your hopper/marker/ect is currently running. This will give you an idea of how much your voltage is dropping.
For an example:
I had a home built circuit the other day that I was having some issues with (it would work and then randomly not work). I measured the voltage of one of the two 9 volt batteries I had in it: it read 7 volts. When I turned the circuit on and measured again my battery read 5 volts. Looking at the voltage/amperage curves that Duracell provides: http://ww2.duracell.com/media/en-US/...LR61_US_CT.pdf
you can see that at about 6.5 volts the battery dies (the service hours remain constant).
So this means that even though my 9 volts appeared to have some life left, because I was drawing so much current they were actually dying out on me. If I put these in something that drew less current they could probably work for a little while.
2. 9 volt batteries have a good amount of voltage but aren't the best in providing current. The cylindrical cell batteries are much better than this. A good indicator is to look at the "C" rating of a cell and its mAh. You then convert the mAh into Ah (divide by 1000) and multiply by the "C" rating. This will give you your average recommended constant current. For instance an Elite 1500 NiMH cell is 1500 mAh = 1.5 Ah; it's rated at 10C so this means that it will work perfectly fine (won't be damaged) drawing about 15 amps for its entire life span.
For a general rule of thumb: the higher the mAh of a battery, the more current you'll be able to draw for a longer period of time (relative to the same type/brand of battery).
1. I've heard that Lipos are more dangerous compared to lithium ions. I believe that these are lighter overall though.
2. I believe that I've also read that lithium ion batteries high a higher energy density (more power per weight) -but are heavier. In looking around to replace the Duracells in my home-made circuit I found this: http://www.metaefficient.com/recharg...teries-9v.html
and then ordered some of the EBL batteries so we'll see how they go.
3. When it comes (to at least LiPo batteries) they hold their voltage until they die. This is a pro and con. It's good because you don't need to worry about decreased performance: like your marker acting up or your hopper slowing down. However, you now don't have the above issues to indicate that your battery is about the die. So if you're in the middle of a game and suddenly your marker dies you're SOL (hopefully you installed a rip drive on your marker lol).
Finally to conclude: A great place to make (practically the lightest possible -at least for NiMH) battery packs exactly the voltage you want them is: http://cheapbatterypacks.com/customp...ks.aspx?mid=20
. They have NiMH, NiCD, and some Lithium cells that you can get stacked in numerous orientations with different wires, connectors, etc.
If you have any questions about any of this feel free to message me! I'm still learning too but if I don't know the answer I'll probably be interested in finding it out myself.