If your battery is going flat in a few days, you have a problem. Either the battery is shot, or you have an electrical problem allowing the battery to discharge. Easiest way to check is to disconnect either cable from the battery. If it still goes down, the battery is shot. If not, start troubleshooting the electrics. If you have an electrical problem, the new battery of whatever type and wherever located will not cure it.

I completed this mod with some great success.  I used an AGM battery, and it works well.  It has enough CCA to turn the bike over easily, but significantly less Ah.  Don't leave the battery on for more than 5 minutes and you'll be fine.

The Li ion batteries that are now available should be even better choices.  You should be able to find a battery with comparable CCA and Ah to the stock battery in a similar sized package to the AGM batteries.  Some of them have special balancing circuits already installed, so they don't require any special care.  The only thing about the Li ion batteries is don't ever let it FULLY drain.  One time will kill it.

Back to the mod...  I kept it mine on the swingarm bracket.  It's made out of 1 1/4" strap steel.  Rather than welding threaded rod to the bottom, I pressed a carriage bolt through the steel and ground most of the head off.  I didn't weld a strap to the back of my battery box, so when I have to take it out all I do is remove a zip tie.  Use some rubber like a bicycle inner tube to insulate the battery from vibration.  I also did this mod WITHOUT extending any of my battery leads. The negative lead was relocated to one of the former battery box mounting holes.  For the positive lead, I relocated the solenoid onto a bracket I made from the left side of my air box.

A clear shot of the solenoid:


The wiring all tucked away neat.  You can also see where my negative terminal is frame mounted:


A look at the outside of the bracket.  Here you can see where the hardware mounts:


Any other specific questions?

I didn't put my battery where the airbox is.  I put it below the swingarm and behind the engine.  You can see the blue zip ties holding it in if you look just above the muffler:



A shot of the battery from above:



One of the reasons I did this is because I plan to make a tool storage box out of the right side of the airbox.  Here are some pics of how I cut it:




It will still mount from the bolt on the top:



My thought is to make it out of fiberglass, I just haven't done it yet.  The side cover and airbox door will still be held in with normal phillips head screws.  For me, this is fine as I always have my leatherman on me.  The tools in here will be wrenches, more screwdrivers, a small fuel siphon, and a few other things.  I mostly haven't done it yet because I don't know how well the fiberglass will stick to plastic.  I figure I'll take it to a boat body shop and ask a few guys for advice since they should all be fiber-gurus.  Again, I've just been too lazy to do so.

Sometimes when it's below freezing, she'll turn a bit slower when you start.  Never any problems, though.  If I leave the bike sit more than a week I plug it in to my trickle/float charger just to be safe.

FWIW: there are actually two zip ties there, each connected to the other.  The only metal they touch is the spot shown in the picture, but on both sides.  The battery is triple layered in inner tube rubber, and that provides good vibration insulation.  There's not much light there at all, and it's not hot enough there to damage the battery - let alone the zip ties on the other side.

I pulled the battery recently to check over everything and replacement some corroded terminal hardware. (I didn't spray apply any protective fluid when I installed it.   )  The zip ties weren't cut, brittle, or damaged in any way.  They sat there for over a year without a problem.

I'm all about over-engineering things.  I feel that this is juuuuuust right.  

HondaLavis drill some holes in the plastic so that when you add the resin it will have places to get a hold from, two holes near each other will increase the hold since it will have more points to build strength from. Basically you are making holes and filling them with the resin to make a virtual dowel into the plastic  

ah right so it's mounted where the emissions breather tank thing is.

when you remove that, how you do route the breather tubes?

Also, what dimensions does the smaller battery need to be?

I was talking about running a strip of ( pick something) around the inside, across the cut, epoxy.. thin metal would glue on with some good epoxy, holes drilled in the metal.