Greeting
I hope u r doing well
I recently got a 10 scale rc truck with a brushless setup.
It has a 4000kv motor and a 45A esc.

I got myself a new 3300mah 11.1 Lipo and a very very basic charger that uses balance port for charging lipo.

Now where i messed up was, when i was connecting my lipo balance port to the charger, i accidentally connected it upside down (or opposite way).
Immediately i felt burning smell coming from the charger
And since then it is only reading the 3rd cell on the lipo and not the 3 green lights like it was usually.

I took my lipo to the truck and that is also not turning on the esc.
So i am confused which one amongst the two i have burned.

Can u guide me as to what should i get? A new lipo or new charger?

Problem is i dont jave even the basic electrical equipments and these batteries and chargers are exorbitantly expensive and hard to come by.
Any help will be highly appreciated.
Much thanks

Was the charger plugged in to a power source when you connected the battery?

I fried a 1s parallel charging board by plugging the batteries in before connecting the power source. Leftover juice from the batteries cooked some of the connections on the board. Lesson learned.

Take this with a grain of salt... but I've been plugging my 1s batteries into the charger first for a while without issue. Granted it's a little usb thing that I connect directly to an AC/USB wall plug. 

I also found this link to charging with parallel ports and such -> https://oscarliang.com/parallel-charging-multiple-lipo <- Unfortunately, it mentions copper traces getting burned away because he connected the balance lead the wrong way.

At the very least you should get a new battery. I'm sure you would have bought another eventually. If you are brave, you can take that new battery and plug it into the charger to see what happens. Do at own risk.

Do you have a multimeter? You can test the cells of your battery to make double sure a cell is fried.

Maybe take some closeup pictures of the charger and battery mentioned?
You probably need a multimeter to determine what's actually damaged. Guessing is not the best option here.

Guys, Guys, the OP's battery is a 3300mAh 3S LiPo three cell pack and 1S info is irrelevant and misleading.   

FIRST, that size/power can make a decent sized house destroying fireball. Do any testing outdoors and away from property. Its currently a suspect battery pack until proven otherwise, so do NOT have it anywhere where if it failed without warning to a short it'd go into thermal runaway and burn you, yours, or your property.

Do not test further by trying to use. You WILL need a multi-meter. If you cannot borrow, there are cheap ones available from dollar/pound/thrift stores.

A balance port only charger is usually neither expensive not difficult to source, its the sort of low budget end item that's supplied "free" with a model. Its simply not worth and too risky trying to test and repair it.  

That type of charger (or a little better) should be easy and cheap to replace, but then we don't know where you are country/locality nor your budget TO replace it, as that is what is likely to be needed.

The LiPO  "should" have survived, but its balance port may well be damaged.   Balance ports and sockets are polarised to prevent wrong way round connection, it should not have been possible for you to do so.

I assume that the main connection battery to model is a larger two pin (XT60 or DEANS, etc). 

To get any further, we need:-

Close up photo of the battery balance plug and its main power plug.  Photo of the model connector.  Pics of the charger and its connections also would help source a replacement for you.

Please be careful!

You probably smoked the charger. The battery would have probably exploded if it was the other way round.

Guessing you have a charger like the SkyRC e3. I have several of them. If you smelled burning electronics, the charger is probably toast.

So you should probably get a multimeter and check the individual cell voltages, first. Then buy another charger.

Oh and pay more attention next time. If a battery goes boom, you are going to know about it and if you aren't charging safely, the resulting fire may well burn your house down and at the least the acrid smell from the fumes will make you want to sell your house.

From what I understand, you hooked your balance plug backwards/reverse polarity. + and - between the battery and charger probably killed or damaged your charger and possibly your battery.

I would not trust the battery or the charger…until they are checked for functionality. If you have another battery you could always see how the charger works with a different battery. Only try this in an area, preferably outdoors, that is away from anything combustible.

If it was me, I would trash both the battery and the charger. Chalk this up to a lesson learned and pay better attention when messing with your batteries in the future.