I switched to a bigger Interstate brand battery, since I had read from I think the Fit Freak forum that such a small OEM battery can die pretty quickly if you leave the radio, or headlights on for even a short period of time. It actually happened to me once when I left my headlights on for a not very long time. Once I noticed my car wouldn't start, I realized my headlights were on, so I immediately turn headlights and radio off. Then this last winter our temp got down to below 0 degrees, and my small battery would not start my engine, so I replaced it with a bigger more powerful Interstate battery to stop that problem (see the link below how to fit a bigger battery). It started right up.
Here is a link below to fitfreak.net forum, where I did exactly as this person did, adding a bigger Interstate battery with way more powerful cold cranking amps.
Wow, first thing... what's causing your battery to drain so fast? Alternator going bad? Crappy stereo/amp install? Take it to the dealer, it should still have some warranty left on it. If not, buy an Optima Red or Yellow top battery.
The battery that is in the first Fit model, that ended in 2008, is very hard to find. I have three auto parts chain stores close by and none of them stock this battery. I had to get it from the Honda dealer.
In April of 2010, the battery was finally replaced by Honda dealer who sold it to me...I had to be extremely persistent ( after being jumpstarted numerous times and driving the car there, they would check the battery and claim that the cells were still okay, inspite of the fact that the battery would die every 3 days)! I found out by mechanic, that the battery for the Honda Fit is not 'aftermarket' as of February of 2010...I don't know if one can now purchase this type battery at your popular battery stores (ie. Sears, autozone etc...). Luckily the battery was still under warranty....in April of 2010 the Honda dealer tested the battery again and said the fuel cells were no good.....thus they changed the battery...We've gone thru cold weather and a blizzard recently where the car once again had to sit for 3-4 days (our streets were not duggout for days thus one's car were literally stuck in the snow). The battery has started up fine ever since the new battery was installed. I wonder if this type of Honda is a 'winter' worthy car in the first place...they shouldn't sale this car in winter climate states!