So I bought a few letters light that works with 2X AAA batteries and i am trying to connect them together to one AC source instead of using batteries. I opened one of them and there is nothing but the lights and the power on/off switch. Can I connect all the positives together and all negatives together? if so, how much AC power do I need? is it 3V or the total of the used batteries? I have 14 letters that's mean I need 28 batteries. 
Electrical Lighting – How to Connect Multi Battery Operated Light to AC Source
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THIS IS NOT A JOKE- THIS APPLIANCE NEEDS TO BE INSTALLED PROPERLY
This is how it should be wired using 220-240volt
BUT
There are some things to consider first!
The wires you are using to connect to .. are they the provided wires? there should have been a solid copper U bridge to connect L1/L2 to each other too!? Where is it?
If that is not the original cable you must consider using 2.5mm solid core cable
But also the wire that is in the plug should be the same/similar type! and it should be DEDICATED ONLY meaning no other plugs on that line
Before the stove you need an isolation switch (any electrician that says this is not needed is a bad electrician!)
And MOST IMPORTANT
A 8AMP (MAX 1700WATT) on 2.5MM Solid Core Dedicated Line!!!
Be warned if you do not meet these requirements you are putting your self at a electrical fire risk - and this is for ALL 220VOLT Installation anywhere in the world. If you have ome insurance and it burns down and they find that your new stove did not meet these electrical rules.. sorry - insurance void!! Even after installation you need a NEW electrical test certificate to certify there are no GROUND leaks! or micro shorts!
Am I missing anything? Is there a piece of equipment I'm overlooking?
Yes. Large solar panels can be bought individually rather than cobbled together from smaller ones. These are designed to feed from the panel as-built rather than having to be modified. Example here.
So what you need to do is find a low voltage garden light system (perhaps one powered by the mains as suggested by @longneck) then replacing its mains voltage converter with a feed from a battery pack charged by the panel. The battery packs could be central or at each light.
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Best Answer
Interesting question: Yes, you can connect all the letters in parallel. But be careful here. You're talking about both AC (mains powers) and DC (batteries). Measuring DC current is more difficult than AC. with AC you can just put a DM with an amp clamp around a wire and whamo samo, you have a current reading. Measuring DC current is less common, possible, but just less common requiring a specialized meter.
Also, your power supply must convert from mains power to 3 volt DC, preferably with some capacitors to smooth out the supply. your lights might not work right or flicker without a high end power supply.