Definitely a lot of variables affect battery life. Area temperature (where you drive) and surface (what roads you drive on...rough/smooth... batteries don't like to be jarred...) are a few, from my experience.

 

I suggest getting a voltmeter:

One thing that I discovered is that the Fit, like other hondas, has a 'low power' mode. When the electrical load drops to a certain level, the alternator actually reduces it's output and you drain the battery! There is a chip called the ELD, electronic load detector.

What I found is your alternator actually puts out LESS juice if your running no lights, no heat/ac. The car tries to save gas, by cutting your alternator output. You'll see this happen if you have a voltmeter, which will show a voltage drop from 14+V to 12+v while sitting idle/ driving with no lights/ac. As soon as you turn on the ac or lights the voltage will kick back up to 14+.

If you spend a lot of time driving with your heat/ac and lights off you might be draining your battery since it will be in low output mode and not charging. I guess Honda engineers did this to save gas and alternator wear.

The other thing you might want to try is a getting a solar panel, or plug in the wall 'battery tender'.

 

I have the 2007 Fit and my first battery died at about 2 years and was replaced under warranty. The second one started getting weak 2 years after that so I replaced it with a Bosch battery from Pep Boys. It is still going strong. This will be the third winter for it. I drive 35 miles to and from work five days a week. I have an amateur radio transceiver that I use during the commute and doesn't seem to affect this latest battery. I hope it keeps going. I'd hate to think about having to replace it ever 2 years.

 

I found this thread via Google. Last month we left the car door open all night, and last night the dome light was left on. We hit it with the jump starter charger for 15 seconds both times and went on our way. It's the original battery from April 2006! Almost 7 years. It gets driven a lot.

 

No it's not right. But I don't know that "something serious" would have to be wrong with the car. In fact it could be something minor. It's obviously difficult to detect, because the dealer took a couple of whacks at it and found nothing, and by now I'll bet you've had at least one other shop take a look at it too.

I'm thinking in two different directions. 1) Overcharging. Batteries don't like it. But it's pretty easy to diagnose, and I would think that someone would have noticed that by now. 2) A starter motor that takes more amps than normal. This might make it so that an otherwise mid-life battery will not have the amps to turn the engine over.

Whatever it is, it is out of the ordinary. (I'm another one still using the original battery after 80K miles and 4-1/2 years.)

 

The problem is a seriously poor battery; the only Honda difficulty is whoever specified the battery, put it out to bid, and failed to have appropriate supplier testing and manufacturing quality standards that Honda usually requires. Its too late for checking our failed battery (Honda retained it) but I'd be curious if anyone had battery failure and knows where was the battery manufactured. Should be encoded somewhere on the battery housing.