My YZT14S has started to show its age so I thought I'd get a fancy replacement. I ordered an EarthEx ETX18C. The battery fired the bike right up. I took it out for a ride and did not get more than 400 yards from the house before the bike died. The dash went dead. I pushed the it home, did nothing but turn the key back on and it started right back up. Testing with a volt meter it bounces between 13.8 and 14.2 at idle. If I rev the bike repeatedly the battery voltage starts to fluctuate then drops to zero.Bike dies. Made sure all fused and connections were okay. If I leave the bike sit for 5 minutes, the power will come back on and it will restart. I put the old battery back in and it seems to be okay. Go figure??

I'd dall Earth X. I'm sure they will send you a replacement.

I put one in my SD and it's been working great for 7 months...even if the bike sits for 2 months while I'm out of town. Hit the starter button and it fires without hesitation...every time. Never been on a charger.

I also put one in my Yamaha desert bike and it lasted one ride then wouldn't crank the bike. They said they'd gotten a bad batch of cells and sent me out a new one with a call tag for the old one. Pretty good customer service.

I shot them an email and they are putting another battery into the mail for me. Great service. My only worry is that it's not the battery, it's voltage regulator. I am thinking I should be looking to replace that as well.

The EarthX still starts the bike right up and still sits at a full 13.5v. Wondering if the regulator is spiking the voltage and the battery is shutting down (fault protection). We'll see what happens with the new battery.

Well, here's the latest. They sent me a second 18C battery. Along with that I also installed a new regulator....just in case. Same issue. Bike fired right up, but If I rev it up a handful of times the battery voltage drops to zero and the bike shuts down.

Their customer service and engineers have been exchanging emails with me almost real time. Pretty fantastic from that point of view anyway. They did a load test on the first battery I installed (and returned) and it tested within their spec but to the low side. I did not ask for details on exactly what that meant.

They are sending me out a 24C (a bit more costly battery) at no extra charge to me. The issues I described to them apparently sounds like an undersized battery for the application, even though they have a lot of 18C's out there in SD990 applications and it’s supposed to be the cross for the 14S battery size. I guess we’ll see. Now I have an extra regulator

There some other issue mate, if the battery is faulty it would more likely not crank, not the issue you are having. Same for a to small battery, it would fail to start.
I suspect and electrical connection or issue. Some posibilities for you to check.
Angle sensor (stops the engine when you crash) sits in the headlight and is prone to problems. (when it's faulty the engine starts but then dies after a few seconds)
The negative cable to the battery, it has a second wire which breaks and it is under the heatshrink.
When it stops does the power to dash and so dies to or does it just stalls?
Also have a look at the main relay, it is fixed to the battery cover, make sure it's all plugged in and the fuse is fine.

You did put in the battery the right way didn't you..?

Well, lets start with your last thought first. I think I got my pluses and minus' in the right places It starts just fine. Fires right up.

I feel like there's another issue too, but here's the rub. If I put the Yusa battery back in it ruins just fine. Always has. It only happens with these new batteries.

Like I said, if I rev it several times the the battery voltage actually drops to zero. These batteries have fault protection that allows them to shut down before they fully discharge in case of short or continued usage (trying to start over and over again) that could cause damage to the cells. When the battery voltage drops to zero, the gauges on the dash go nuts and the bike starts to idle rough then stalls.

If I just start it and leave it idle it will run all day, just like normal. Go figure huh?

Main relay is fine, fuses are fine, tip sensor seems to be fine. As for the ground you were talking about, you mean the ground off of the regulator? I will recheck the grounds but the thing runs just fine on the Yusa battery.

Did you actually run the new battery with the new rec/reg?
Can you do a test with a voltmeter? Put it on the acc connector so you don't have to dismantle the whole thing again.
1-Take a voltage reading without the engine running.
2-Start the bike, let it idle and take a voltge reading.
3-Then give it some throttle and keep and eye on the meter to see what happens when it craps out.
let us know what readings ou got?
If it runs fine on the original bat that is weird!
That can only be two things then: charge voltage too high and the safety in the bat shuts it down ( which is dangerous as it could blow other things up, like disconnecting your bat with engine running) Or the bat is faulty and/ or doesn't like the SD charging system
I have one of these antigravity lipo bats and never had any problems. I got it from the US, put it in and fine ever since.

Yes, ran the new battery with the new reg.

I have run it with a voltage meter. Testing with a volt meter it bounces between 13.8 and 14.2 at idle. If I rev it up it peaks at about 14.7. Nothing I am seeing on the meter strikes me as out of range. I'll post up what happens with battery number 3 when I get it tomorrow.