Reddit reviews Venom 20C 2S 5000mAh 7.4V Hard Case LiPo Battery with Universal Plug (EC3/Deans/Traxxas/Tamiya)

Ah, damn. Yea. It's not terribly difficult to solder, but you do need to be careful that you don't short the battery.

Uh can get all the soldering equipment you need for under $50.

Otherwise, venom makes a decent battery too: https://www.amazon.com/Venom-5000mAh-Battery-Universal-Traxxas/dp/B000VUF3O2

And it has adaptors to deans so no soldering needed.

DEFINITELY. This battery will last you about 30 mins and will make your truck fly like a rocket. Source: Have a 4WD Stampede and 2 of those batteries.

Honestly, I've had no problems with a knockoff Imax B6:
http://www.amazon.com/Eastvita%C2%AE-Battery-Balance-Charger-Batteries/dp/B005EF15Q4/ref=sr_1_1?s=toys-and-games&ie=UTF8&qid=1420243653&sr=1-1&keywords=imax+b6

Note you will need a separate 12v power supply, like so:
http://www.amazon.com/Intocircuit-Adapter-Charger-Benq-Monitors/dp/B0023Y9EQC/ref=pd_sim_t_1?ie=UTF8&refRID=029TBSHJ9V4B4E3QT29A

As far as battery connectors, you do bring up a good point. The non-traxxas chargers will include a variety of adapters, but none that will directly fit traxxas connector batteries. If you have access to a soldering iron, you can convert your traxxas ESC over to a standardized plug (since you will have the same issues with the batteries). Dean's is what many people use. Theoretically, the traxxas connector has a little more surface area, but in practice, it's not relevant. Your local hobby shop can also do soldering for you. It is possible to charge batteries by just clipping alligator clips onto the terminals, but this is tricky with how concealed the traxxas connectors are.

Regarding batteries, there are three important specifications:

1. Voltage. 2S is 7.4V, 3S is 11.1V. More voltage = more speed = more heat = more likelihood for driveline failures. I would start with 2S; still faster/more consistent than NiMH
   
2. Capacity. Expressed in milliamp-hours. 5000mAH is a good balance of size/expense/runtime
   
3. Peak discharge rate. Refers to how much power the battery can supply based on demand. The peak wattage figure for the Velineon system is 722 watts at 3S, which is around 65 amps. You obtain the amperage by multiplying the C-rating of the battery by the number of amp hours. So a 5000mAH battery = 5 Amp-hours x 20C = 100 amps peak discharge rate. All this to say, a 20C battery should be more than enough for your truck if you buy the recommended 5000mAH. The advantage of these batteries is that they have traxxas connectors if you don't want to do any soldering on your batteries: http://www.amazon.com/Venom-5000mAh-7-4V-LiPO-Hard/dp/B000VUF3O2/ref=sr_1_6?ie=UTF8&qid=1420243945&sr=8-6&keywords=venom+battery+2s
   
   A slightly smaller capacity, but a 2-pack: http://www.amazon.com/Venom-4000mAh-Battery-Tamiya-2-Pack/dp/B00FE0S4NQ/ref=sr_1_1?ie=UTF8&qid=1420244636&sr=8-1&keywords=venom+2s+20c+2-pack
   
   
   Edit - if you end up being able to get your batteries from someplace that's not Amazon, I would recommend these: http://www.hobbyking.com/hobbyking/store/__58916__Turnigy_5000mAh_2S_20C_Lipo_Pack_AR_Warehouse_.html
   Given that they are inexpensive ($18) and perform just fine.