Right, I see what you mean now. The motors will try to draw more than that battery can provide, you probably want something sub c, like this:

http://www.ebay.co.uk/itm/12v-NiMH-3300 ... 336e797b7a

I use those escs in Eric Jr, they're ok but a bit on the cheaper side of things, if you're on a budget and just looking for something that runs then they can be good. We get away with running them at 14.4v for a little extra speed, if you want to do that you would want to use a battery similar to this:

http://www.ebay.co.uk/itm/14-4v-3700mAh ... 3353ee4262

Or, 2 of these:

http://www.ebay.co.uk/itm/7-2V-3300mAh- ... 336e7982cb


But for a first robot 12v will get you going at least and it is a little bit cheaper too