The problem is, the YFZ doesn't really have a charging system, it is more of a "maintenance" system. The '04(and some say '05 as well) model year doesn't charge the battery unless you are revving the motor or else putting a drain on the system(lights on.) I have an 04 and an 05, both with the battery boxes modded to accept a 12BS battery. I currently have Walmart everstarts, 1/2 the price of the Yuasa's. The 9BS is close to stock size, but the 12 has more cranking amps. All you have to do is cut the rear wall all the way off on the battery compartment. Take your time with a utility knife and some long pliers and it will come out OK. If you use the 12, it is a taller batt, so the bracket that sits over the battery gets squished down a bit, but it DOES work. If you don't mind remounting a few components that hook up to that bracket, you could run a 14BS and have even more reserve. To solve your battery problem, you either need to run with the lights on or install the Yamaha light eliminator kit which basically adds resistance to the system and simulates the lights on. Finally, and this really applies to all the 450 class quads as far as I know, you should be putting a battery tender on it between rides to keep it at max reserve power.

 

<div class="FTQUOTE"><begin quote>Originally posted by: Koopa


I've also been hit with the other manufacturer flaw. Decompression plug popped out about 6 months ago. :\ If you havn't had that happen I would replace it before it does. Nobody warned me.</end quote></div>

Yeah... I waited til mine popped out before I fixed it unfortunately... happened a few years ago.

 

x2 on the Yuasa batteries, OEM is the way to go for those.

 

You will go through a everstart every year nomater what you have i just keep buying one for my warrior ever year because there onley 40 bucks. They cant handle the offroad vibration of a atv and it welds the plates together inside the batery.

 

http://www.odysseybatteries.com/ try one of these, put one in my ds in 03 i think it was, never touched it since only a tender in the winter, there a lil spendy (think i paid 150 for mine) but worth ever dollar and they have really good CA's

 

yup, pick up any AGM style dry cell battery as the ones wall mart has cannot stand up to vibration- and most quads, bikes, lawntractors dont have much of a chargeing system so order a Yuasa 1amp charger and charge it after every ride [img]i/expressions/face-icon-small-smile.gif[/img] Im still on my first Yuasa from 1995 in my trx200sx by chargeing it a few times a year [img]i/expressions/face-icon-small-smile.gif[/img]