battery chargers

I don’t have a way to upload anything.  Maybe because I’m new or this forum doesn’t support it.  Basically, you need to take the 18 volts coming in.  Branch that off to at least 4 individual resistors, one for each transistor.  Low values like 0.1 ohm given the currents you have.  You could even use a 0.02 or something if you can find them.  Then feed each resistor to a individual transistor on the collector pin.  For the base, put two 6.8v zeners in series with one connected to the base and one to ground.  Take a resistor, 220 or 330 ohm should work, from the 18 volts to the base/zener connection.  That will supply 13.6 volts to the base.  The base/emitter will drop close to .6 volts which will leave you with a output about 13 volts.  Then connect all the emitters together for the output.  You could add some capacitors if you like.  That depends on what your batteries may need.  If you want it to output 13.6 volts at the emitter, you could have a diode between the base and zener.  That will offset the base/emitter voltage drop.  If you want to really reduce ripple, put a capacitor, 2 to 4uf or so is fine, from the base to ground.  

I hope that makes sense.  A picture would be nice but can’t do that here.  I might add, having four of the transistors will put a full load on those transistors.  I’d suggest having 5 of them.  Give the some breathing room current wise.  If you can handle it, 6 would be even better.  You also need to heat sink those very well.  They will dissipate about 300 watts for all of them.  With 5 transistors, that’s about 60 watts each.  With 4, about 75 watts each.  Those wattage amounts are just a in my head estimate.  

This is kind of a very simple and basic thing.  Just be careful about wire size and such.  Lots of current.  

@dalek Hi, this forum does not host picture that’s why you cannot find a way to attach it but if you use pics host websites such as IMGUR (you-ll need to setup an account first) or postimages.org Were you wont even need an account to do it and then copy paste a direct link in your post the picture will in fact appear in your post as if embedded in your post. Fairly easy. alternatively you can share links to a desired picture in google drive err…but is a long winded process as and access needs to be granted by you every time someone clicks on that link. I’m sure there is an entire list of picture hosting websites that one can find and they will all allow it to work here. I hope it helps.

@ovi4  I kind of figured the site just didn’t have the feature.  I found a link to this site on Youtube.  It seems to be more of a personal site and not a commercial site.  Funding a site with personal funds is more of a challenge and being able to upload images, videos etc adds to that cost if they are served by this site instead of external links.  I can understand not having that feature if this is more of a personal funded project.  

I have a account for images but it’s at its limit already.  I don’t want to delete any images because if I shared them somewhere that just links to those images, that image will be gone.  I’ve ran into that in the past.  Find a place that has a answer in a image and the image is no longer available.  I hate that.  I don’t want to be one that does that either.  

So, the best I could come up with, explain how to create one by explaining what is connected to what.  I think I explained it clear enough.  If the OP has a way to draw it out and post a image or something, I can confirm if it matches what I explained or not.  It’s a rough design tho.  It should work as is but some improvements could be made if other features are needed.  I actually did a rough circuit in KiCad just for giggles.  

I’m hoping to hear from the OP as to whether this helps or not.  Could be they already found a solution.  One could google a buck power supply easily enough.