[...] do I really need all that power someone told me to get as much as the board could safely handle which is 12v but the only thing that I am running off of the UNO itself are the transistors for 2 h-briges (although I'm thinking about replacing the steering mechanism with a servo) and 2 IR proximity sensors and maybe an IR module on top to make it act out preset commands via remote. The whole project is going to be very light 3-4lbs max. and the drive motor is pretty small I am using the 5V plug off of the UNO to power it but the original system was 4.5V. Thanks again for the info and saving my house I'm not sure how my roommate would have handled that
No, you are much better off sticking to only the 2 cell lithium (the 7.4V battery).
Your Arduino and the stuff you added all run on 5V, the Arduino has got an LDO regulator I assume, which means that it needs at least 6V (perhaps a little more) to stay in regulation.
If you feed it with 12V, there's an excess of 6V * [current draw] of heat to get rid of. If you add a servo, 1A of curernt draw is fairly realistic and makes it easy to calculate the power lost to 6V * 1A = 6W extra
(there's the ~1V * 1A = 1W that you can't do nothing about) that you have to get rid of, needs a hefty heat sink on your regulator.
This extra 6V is doing nothing for you at all.
Your two cell lithium is 7.4 (probably around 8V right out of the charger), so the excess voltage is much smaller. at 7.4V there is a total of 2.4V * 1A = 2.4W to dissipate.
While the battery discharges, the voltage goes down towards ~6V, which is just perfect for a 5V LDO. Power dissipation goes down linearly with the voltage and at ~6V you have the minimum drop possible (and around 1W dissipated.
he above is all assuming a constant draw of 1A. In real use it will vary and most ofthe time it will be less, but the voltage/power relationship mentioned still holds.
On a slightly different note...You seem to confuse power (which is V*A and is termed Watt) with voltage and this tells me that you are not ready to build your own charger.
However, you'd do well in making a voltage detector (either implemented in your microcontroller via A/D-C, in an op-amp, or by one of the very simple to use voltage detector chips. This way the robot knows when the battery needs to be recharged and that's very important, as if you discharge a lithium too far, you ruin it (with the risk of having your very own personal fireball).
You can easily charge the battery while it's powering your electronics, but you're up and running much faster with a spare to swap in.
If you want it to charge on a pod of sorts, connect a reliable charger to a base with a couple of bronze leaf springs for contact with a couple of contacts on the 'bot and make arrangements for it to hit the right spot - a contact pressure of 10..15oz should work with the weight of your 'bot and make reliable contact.
Another way is a connector that you have to plug into the 'bot - I like to use 3-prong XLR's as used in pro audio (4 prong versions for when I want feedback), as they can handle the current well and are locked together, so they won't accidentally fall out (unfortunately, the cheap versions are crap and the good ones are pretty expensive compared to other connectors).
Even a Phono (RCA/Cinch) plug and socket can be used, or obviously, a DC connector, but he latter is the most un-standardized connector, so it may be hard to find good matching male and female connectors).
By charging this way you loose the protection that thermo-detectors give in good lithium chargers and you need to make sure that your charger can work reliably without it (or you can add one to the battery yourself if you know how to connect it to the charger)
[...] Had to explain that not only was I not making drugs but it was not going to blow the house up either.
And that's when your room mate rolled over and dozed off out of boredom - you have to keep a certain amount of mystique