Konrad,
Short answer: Cubs use the battery as a Voltage regulator, and the battery salesman informs us the Scorpion brand AGM battery has a brief 15 Volt charge limit. Your Cub likely surpassed that limit on the long ride, and the battery performed exactly as designed. It failed, and it should have failed, and it is not the battery maker's fault.
It is simply the wrong battery choice for the long distance Cub rider. Long answer below, explains my opinion.
Jon Pardue
Sarasota, Florida
Long answer: Most motorycles have a Voltage regulator, but several small Hondas lack them. I'm not here to scare anyone out of buying a product, but your AGM battery failed for a reason, and I readily blamed the AGM design inability to withstand a prolonged over Voltage charging condition. I am wowed at the specs the seller claims for the Scorpion battery, so they move to the top of the heap for AGM design. Still, I stand by my assessment and opinion, because my logic and reasoning are based on the facts at hand.
I like AGM batteries, but running one in a stock Cub in my opinion is a mistake, based on other members, customers, rider experiences plus my own R&D work. My opinion is specific to the Honda Cub.
The seller stated "You may want to check you source for your information. They apparently have no idea what they are talking about or are blatantly lying trying to scare you. AGM batteries can handle charge voltages in the range of 14.4 to 14.8V continuously and over 15V for short duration with no harm. They can be treated the same as conventional lead acid batteries."
Lacking any motivation to lie or frighten you, or to cheat the Scorpion seller out of a sale, the fact is we have no Voltage readings from your bike at the moment of failure. We have forensics evidence you supplied: your battery blew covers off and dramatically lost Voltage. I opined the charging Volts were too high, based on my experience with measuring Volts on Cubs and encountering destroyed AGM batteries.
Yeah, the battery could have been defective, but that seems unlikely since it had some time on it. And what exactly is a "short time"? You had a 60+ mile ride, so you might have had half an hour of 16.5 Volt charging. I bet that battery held tough for quite a while.
If your headlight bulb blew, there may have been 20+ Volts at the battery. This would have quickly exceeded the unquantified "short time over 15 Volts" parameter and caused battery failure.
The seller continues with "There is a higher chance of a conventional battery catching fire or exploding, as it constantly vents its hydrogen gas into the atmosphere. If a wet battery is overcharged not only will it vent hydrogen it will spew out acid."
Those verbs and adjectives sure sound scary, but we all see how the vent hose innocently routes battery gas and acid to the ground.
Honestly now, has anyone seen a hydrogen fire at the end of the vent tube on a stock Cub? I have not, yet. Most everyone here has probably seen paint and metal damage caused by a missing vent tube. I have seen a lead-acid car battery explode during a start, when the Amps delivered were highest... went off like a bomb. It said so right on the battery - may explode. Never seen a stock Honda battery explode - yet. Never seen an AGM do anything but expand some.
Finalizing, we get "Scorpion is a good brand, it may have been a weak or faulty valve or your charging system may have gone awry. I would chalk it up to a fluke or that something external to the battery was overcharging the battery. But there is absolutely no truth to what this gentleman shared with you. All the available literature online would support what I have just explained."
The Cub charging system is something external to the battery that will gladly overcharge the battery. While the seller has an awareness of AGM battery literature, and surely means well in defense of the good qualities of AGM batteries, do you suppose the Honda Cub charging and electrical systems are mentioned in those texts?
The Cub is at liberty to produce charging Voltage in excess of 15 Volts by design, and by design it uses the battery to behave as a Voltage regulator. Honda knew this when they designed the bike, and they designed it around a lead acid battery. While I do not agree with Honda for choosing this methodology, it is what it is, and it works pretty good with a lead acid battery.
The seller's statement clarifies why an AGM battery will not work in a Cub under all circumstances. On average most Cubs probably never hit the 15 Volt limit, so an AGM battery is probably a fine choice for short haul or low-speed riders. Cubs with a weak charging system might barely make 12 Volts at the battery, no matter the ride.
Konrad, your charging system is probably in good shape, your battery terminals are clean, and while your intent to buy a "better" battery is honorable and good, the battery was likely pushed past its design limits during a long ride on your well-maintained bike.
My C70 has a lead acid Yuasa battery for many good reasons, many learned and reinforced right here by this group. Respectfully, my CT90 is fitted with an AGM battery and a Voltage regulator. So is my Buell X1 Lightning. The C70, CT90, and S90 Hondas have taught me some hard-won electrical lessons.
In the case of the stock Cub, I agree with others here:
Buy the correct stock capacity lead acid battery
Fill the new battery with electrolyte
Charge the battery fully
Use a Battery Tender now and then
Top off with distilled water as needed
Keep all the electrical connections clean and tight
Replace the battery when it will not hold a good charge
Enjoy the ride.
Jon Pardue
Sarasota, Florida
1970-73 C70 Honda Service Manual: http://tinyurl.com/6ebwtw
1970-73 C70 Troubleshooting Guide:
http://tinyurl.com/6ebwtw (scroll to sec.7.1 page 101.jpg)
1980-83 C70 Honda Service Manual: http://tinyurl.com/hu42c
1980-81 C70 Troubleshooting Guide:
http://tinyurl.com/hu42c (scroll to sec.18-1 page 170.jpg)
1982-83 C70 Troubleshooting Guide:
http://tinyurl.com/hu42c (scroll to sec. 20-28 page 205.jpg)
1980-81 C70 Maintenance Schedule: http://tinyurl.com/z4zn6
1982-83 C70 Maintenance Schedule: http://tinyurl.com/hw35c
More resources for C70 Passports and Cubs:
http://www.shlaes.com/Vehicles/Scooter.htm
http://www.velodrome.com/HondaC70/HondaC70.html
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