They are a little tall for the CT box.

I added a note that the Walmart seller might be using the wrong pic so use caution.  The WL version used to be easy to find, not so much anymore.  

Just that little difference of leads out the side makes it fit much better in the tiny CT box.

Also, they might not have the same "overcharge" capacity as a flooded battery.  You don't want to let any lead-acid battery go dead, but anecdotally these alarm batteries seem to last better if they aren't fully charged before you go on a ride if that makes sense.
 

Yeah I get what you mean about not having it fully charged before a ride. I normally don't go for super long rides anyway. Usually it's about 10 miles. I have the lights turned on and use the turn signals, so that drains the battery a bit. If it's a little tall, I think I could lower that box down a bit, but we'll see.

Edit: It fits fine. Just a bit taller, but there's still clearance to the seat pan. My rubber hold-down covers the positive lug, and I put some non-conductive grip tape on the seat pan above it, just to make sure. Nice not having the vent hose now. Came charged at over 6.4 volts.

Not sure if it helps but as you're running with lights on i think there's a double connector on one loom wire to increase night time charging. Might be green into green/red. I'm terrible on wiring diagrams & happy to be corrected--educated lol.
www.yamaha-enduros.com/index.php/wiring-...ct1-c-wiring-diagram

Just FYI, it's normal for a 6v flooded battery to read 6.5v right after charging and then drop to 6.1 to 6.3 within a few hours.  

(12v flooded batteries act the same way but voltage is higher... car battery might read 13v right after charging and then drop to around 12.5 or so after it sits)

What I remember reading is that when the battery is charging, the internal resistance drops.  After the charging stops, the resistance stabilizes and voltage reading drops slightly.

Mark, when I checked it when it was newer, the flooded battery would rest around 6.3 volts. I know it doesn't seem like a lot of difference between 6.1 and 6.3, but my understanding is that at 6.1v resting that's almost a 50% depleted battery. If you're riding around with a battery that can't hold a charge with the lights on, I think that's what led to the bike stalling out at stop lights. I also have turn signals on mine and use them, and they are all incandescent.

I have 12 volt chassis and house batteries in my motorhome, and I'm always checking the voltage on those (have meters on both). Usually they rest around 12.6, sometimes bouncing between 12.5 and 12.6. If they get to a resting of 12.3 to 12.4, that's when I consider that they're pretty much shot. Of course when I have a heater on or something like that, the house batteries will go down to close to 12 volts, but after it turns off they'll bounce back up to 12.5 or 6.

So far, I really love this little AGM alarm battery. Was cheap too!

Three years is a long time on the little CT1 flooded battery so I'm not saying it wasn't time to swap it.  

I am saying that resting voltage of "a little over 6.1" doesn't mean a battery on one of these old bikes is bad.  And I was saying the fact is that it's normal for the battery to lose a few tenths of a volt or more when resting.  (you know that, but others might not). ESPECIALLY if you're talking about after it was charged with your stock Yamaha charging system.  

Use your RV example.  You didn't mention that the alternator and the 120v battery charger probably put out well over 14 volts when charging.  Some 120v "smart chargers" spike to over 15 volts!  

That's the equivalent of 7 to 7.5+ volts for a 6 volt battery.   The Yamaha system is designed without a voltage regulator and you might find 7+ volts at the battery when revving the crap out of the engine, but often the voltage at the battery is below 7 volts while riding around normally.  This is by design.

Voltage is the "pressure" that allows the battery to charge fully.  If you hooked up a 1000 amp charger to your RV batteries that only puts out 12.8 volts, the batteries will take forever to fully charge, if they even fully charge at all.  You must get those volts up in the 14 volt range (7 volt on the Yamaha) to "push" the power into the battery.  

Modern vehicles have voltage regulators set at a high enough voltage to fully charge the batteries.  The voltage won't go higher.  Once the battery is fully charged, the charging power is reduced.  

Your Yamaha does not have a voltage regulator on the battery charge circuit and without enough load on the charging output, the voltage can spike really high (which is why bulbs blow).  The battery itself is used as a crude "voltage regulator" and may never fully charge while riding.  Again, this is by design. 

I'll start another post to explain my theory of how using the battery to regulate voltage works on these bikes.  

The Yamaha charging system is a "fixed output permanent magnet alternator".  I'm going to make some numbers up here for illustration purposes.  Let's say that at 7,000 RPM, your Yamaha CT1 alternator generates 24 watts of "nighttime charging" power.  Since it uses permanent magnets of fixed magnetic field strength.  That output is fixed.  It will put out 24 watts at 7,000 RPM.  Period.  Lower RPM means less output.  

(The voltage regulator on a car alternator powers variable strength electromagnets.  So if less power is needed, the regulator cuts back the input to the electromagnets which reduces the power output of the alternator.  At 4,000 RPM the car alternator can put out zero watts or maximum watts depending on how strong the voltage regulator powers the electromagnets)

Basic formula for electric power is Watts = Volts x Amps.  Which we can use math to rewrite as "Volts equal Watts divided by Amps".   Using our example of a 24 watt CT1 alternator output at 7,000 RPM, to get down to 6 volts we'd need 4 amps of power to be used.  (6v = 24w/4a). If the amps used drop, the voltage rises and vice-versa.  

In other words, the CT1 voltage is controlled by the amp load on the system.  Which is why when one bulb burns out, often others follow very quickly.  As the bulb load is reduced, the system voltage rises.

So how does this make the Yamaha battery into a crude voltage regulator?  

In my last post I mentioned you need voltage to "push" the power into the battery.  Voltage acts like pressure.  If you have a battery at 6 volts and a charger that puts out only 6 volts or less, no power can flow into the battery. 

A good analogy is a tire and an air compressor.  If we say the battery is the tire and it has 6 psi in it, if we connect an air compressor tank with 100 psi, that air is gonna flow into the tire!  But if we have 100 psi in the tank and a regulator on the output hose set to 6 psi?  No air will flow into the tire.   Similarly, if you have a battery with 6 volts in it and connect a power supply with 100 amps that's regulated to 6 volts, no power will flow into the battery.  

Also similarly, the higher the voltage (or pressure) difference, the more power (or air) is going to flow.

So now we have our CT1 spinning at 7,000 RPM making 24 watts of power. If the charge wire is not connected to the battery, the voltage coming out of the stator battery charge wire is going to be pretty high...  probably in excess of 20 volts.  When we connect that charge wire to the 6 volt battery, that 20 volts of "pressure" is going to push the power into the battery just like the 100 psi in the compressor tank would push air into the 6 psi tire.  

Since the max output of the stator is limited to 24 watts, the current flow into the battery is going to drop this voltage.  Using our formula above, at 3 amps of current flow into the battery the voltage will be 24 watts divided by 3 amps = 8 volts.   (6 volt bulbs can usually handle about 8 volts).  

The key here is that 8 volts is going to allow the amps to flow into the battery.  Since the stator output is fixed, more than 3 amps of flow is going to drop the voltage below 8 volts.  When the voltage drops, it's like the pressure dropping so the flow (amps) drops too.  That makes the voltage go up.  Hopefully you can see that if you have a fixed output alternator, the battery can act as a crude  "voltage regulator".

On a modern vehicle, the goal is generally to charge the batteries all the way up and then back off on the charging output with the voltage regulator circuit.

On the CT1, by design the battery can't charge all the way up at lower RPM.  And when the RPM is high and charge output is max, the battery absorbs the amps which keeps the voltage from going too high.  In fact, you probably don't want to have the battery charged all the way because if battery is fully charged that 8 volts and 3 amps of power need to go someplace and it does.  It boils the water out of the battery once the battery reaches capacity and can't accept more charge.  

And again, no criticism on changing the battery in this case.  Just a caution that resting voltage is not necessarily a good indicator of battery condition on these old bikes.  

In fact, I've had batteries that show 6.5 volts resting with no load and with any load, even just the taillight, the voltage drops way below 6 volts.  Load testing is by far a better method of determining battery condition than resting voltage.

Thank you for listening to my Ted talk!  

That's a very good, easy to understand explanation, or Mark Talk . I do appreciate it.

I did and have used a good, small smart charger on that battery over the years, especially if I hadn't ridden for a while,  I also did put a 6 volt regulator on the bike. Back when I first started working on it my headlight blew out, then some other lights did as well. My CT-1 didn't originally have a regulator. But it was after the last charge from the smart charger, then sitting for several hours and it dropped down to 6.1, that I figured it gave up the ghost. I do understand that a load test is the ultimate arbiter, but not worth the time in this case IMO.

As I mentioned, I've seen many forum posts where some people mentioned only getting 6 months to a year out of modern Yuasa batteries. People speculated about the purity of the lead etc. but I figure I got my money's worth out of it. BTW, the house batteries in my motorhome are a pair of 6v Trojan T-105s, hooked in series for 12 volts. They're close to 10 years old now, and still going strong. Basically golf cart batteries. I'm beginning to think they might be on their way out, because normally they would settle at 12.6, and I just got back from a trip and they were settling at 12.5. I'll see how much more time I can get out of them...