Excellent choice of your brother's on the Exo RTR, I'm really enjoying mine, using 3S on the stock motor, performance is definitely good. I had expected a 2 pole motor to be underpowered in a car the size of the Exo but it isn't, it's surprisingly good. On 2S its slightly tamer. Some time in the future, a simple swap to a Castle 1410 3800kv would make the car a real handful and shouldn't need an ESC upgrade, though it might be worth considering one at the same time. The stock steering servo on the Exo RTR is crap, again a 645 or 5645, or the protek would be fine. Replace it before it breaks, it's slow as well.<div></div><div>The radio recommendation stands for the LX, absolutely.</div><div></div><div>The lipo cutoff will simply cut all power to the car, including steering, when the battery reaches a critical voltage, these are usually set to 3.0 or 3.1v per cell.</div><div></div><div>Chargers, yes, the Imax is a good and cheap charger. Consider picking up two.</div><div></div><div>For running in good space, yes, 3S for the Exo and 4S or more for the LX. The Exo does run a nice quick but not fast pace on only 2S, its very satisfying for messing around outside the house without fear of any high speed accidents, consider picking up at least one 2S for such occasions. You will want batteries of 5000mAh ideally, and with a C rating of at least 40, but that size (increases in C and mAh usually mean increases of battery size) is right on the limit of what standard battery trays will accept. The trouble is worth it though. These will be a tight fit, it's not like slotting AAs into a toy car, you may need to sweat a bit.</div><div></div><div>With significant sweating and swearing (you need very strong fingers), I can get these excellently cheap 3S packs into my Exo. It ain't easy and it ain't fun, but once it's in there, its all good. No mods to the stock battery tray or straps, which have a phenomenal amount of stretch on them.</div><div></div><div>http://hobbyking.com/hobbyking/store...idproduct=9962</div><div></div><div>And I'm also able to fit a pair of those (one above the other) in the SC8e's battery tray, which is a notoriously small tray. These zippy packs are actually shorter than stated in the description by a fair amount (for this particular pack, I can't speak for others in the range, but I get the impression that all 'soft' packs have a 'generous' length specified) and can even be slightly squeezed.

So, you want the same cells in a 4S configuration (I've not used these exact 4S packs, but I can tell by the dimensions they are the exact same cells as my 3S and 6S 40C zippy packs that I use all the time) for the LX...</div><div></div><div>http://hobbyking.com/hobbyking/store..._4S1P_40C.html</div><div></div><div>They're both out of stock right now unfortunately, but they should be back in soon, make an account and put them in your wishlidt and you'll get a notification when they're in. If you're impatient, you could gor for a higher or lower C optoin to get you running. Or if you just want something in stock from amainhobbies to get you started and get everything from the same place, these (link below) are the most economical option for 3S, but these packs will have shorter duration, less power delivery and shorter lives, for more money, it's kinda sad really that the only way to get reasonably priced packs is striaght out of China. At least it has a Deans type plug already on it. I forgot to mention that about the zippy packs, you'll need to order Deans style plugs and solder them on yourselves. It's not hard, don't let it put you off. I actually enjoy soldering.</div><div></div><div>http://www.amainhobbies.com/product_...r-111V-4100mAh</div><div></div><div>And for 4S...</div><div></div><div>http://www.amainhobbies.com/product_...-ROAR-Approved</div><div></div><div>The Zippy (or other 5000mAh) batteries will give about half an hour of average running in both cars. These EcoPower ones about 20 minutes, but of course they'll charge quicker too. Reviews overall of the EcoPower packs are surprisingly good, some people are saying they seem to perform better than spec suggests and that they are a very convenient size and weight.</div><div></div><div>The 2650kv combo is a much faster and hotter motor, for 4S use primarily (6S in short bursts only). Basically, as you go up in kv you go up in demands made of the electronics in terms of pulse frequency and amperage draw, subsequently generating more heat. 2200kv, particularly that motor, is a real sweet spot for gearing options and a good balance of torque and speed.</div><div></div><div>As for the battery/esc rating concept you pretty much got it right, however, you should always try to double the amperage required by the motor in the C rating of your battery, the ESC is not an issue at 1/8th scale, they are all very tough as far as handling the current demands. A 100A motor, could actually draw a lot more for a second or two on startup with a car attached on a high traction surface, so aim as high as you can afford with your C rating, hence my recommendation of 40C at 5000mAh (200A capability). Running with batteries of lesser capabilities than about 150Awill strain the batteries and shorten their lives as well as choke the motor for power on extreme accelerations or running in grass. As you go up in C beyond the requirements of the motor, you can still feel a small benefit in punchier power delivery all the way up to about 100C, where the benefit of more C starts to be indetectable.</div><div></div><div>Keep going with the questions, I don't respond like this to every poster as you can imagine, I like your approach to learning and the way you do your own research then ask the right questions, I wish we got more newbies like you. By the way, without meaning to brag, just in case your brother has such designs in the future, that particular car is quite rare and very, very expensive, but hey if you get bit by the hobby, no reason not to go for it one day. </div>