I went to start my motorcycle after a long winter and it, expectantly, did not start due to not enough charge in the battery. I put on a trickle charger for a few days, and it ALMOST started, but lost its charge to quickly to do so. So I put on my real battery charger and left it on overnight. The next day it started, but needed assistance from the battery charger to do so (15 amp charger capacity). Left it on to charge the rest of the day. When I checked it again, the charger gage indicated it was putting out little or nothing. So I disconnected it and tried to start. Absolutely dead. I then hooked up the charger again and unless I turned the key on (on the bike) the charger acts like it’s doing nothing. When I turn the key on, it’s pegs the output to 12-15 amps.
I’m guessing the battery is shot. What’s the easy way to diagnose it?
I think you just did it the easy way. The battery won’t take a full charge or hold it. Did you happen to put a meter on it at any point.
I agree the battery is a goner. Cycle batteries don’t handle nearly the amount of current as a car battery, therefore your full size charger might have been too much for the battery. It was likely shot anyway since the trickle charge didn’t hold.
I’d warn against using your charger when starting the bike, you might damage the rectifier and perhaps worse the stator. Bikes don’t use alternators, which are easy to replace. Bikes use a stator that rotates somewhere inside the motor, some are very hard to change. Meaning a new stator could be a $1,000 job. If you need to jump start a bike, either push it, use a jump box, or use 12V battery that is not hooked up to a charger or running car.
No, I didn’t put a meter on it. Mine went missing.
Never ever use a big charger on a 7 to 15 AH bike battery…two or three amps charging currant at the most, and that only for a couple of hours…A slow charge would be 1/2 amp or less…
Look around in thrift stores for a 12VDC plug-in wall transformer. Cut the connector off and install a pair of red and black alligator clips so you can connect it to a battery. You now have a M/C battery charger. Find a beefy wall wart with 750 MA to 1.5 amp capacity…
M/C batteries seem to self discharge faster than car batteries so to avoid sulfation over the winter, connect your little charger for a couple of hours every 45 days or so and they will last a lot longer…
IBID. And battery tenders will simply boil them (and small watercraft, riding mowers, etc) dry in short order. Trust me on that one. 
Regular chargers of the type that can have the amperage adjusted to low are your best all around bet for most types of batteries, but don’t let it go un-monitored.
Chase
Yep, you have diagnosed a dead battery.
Motorcycle batteries don’t typically survive deep discharge like that, even for short periods. Get yourself a good motorcycle battery trickle charger, and when you or your mechanic replace the battery, install the cable the came with the charger so you can simply plug that cable into the charger next time you store the motorcycle. You can also use this cable for electrical accessories like a heated jacket or vest. My motorcycle mechanic installed the cable for free since he was already installing a new battery and I bought my trickle charger from him.
A few years ago I was collecting bikes and had 7. Keeping the batteries fresh in the winter was an issue. I used a battery tender charger, but rotated it amoung the batteries. I’d leave it on for a couple of days every 2 months, or until the indicator turned green meaning the battery was fully charged.
Bike batteries need water (distilled of course) and have small capacity for water. Some batteries are sealed, but many bike batteries still require removing the caps and filling to keep water levels between the marks on the side of the battery. Overcharging, even with a battery tender charger, can run a bike battery dry much quicker than you might expect.
I lost more batteries due to running dry than any other reason. On a hot day a long ride would drop the water in the battery and some of the batteries were buried so deep in the bike you could hardly see the battery at all.
You can use a light timer to turn the trickle charger on for about 30 minutes a day. That will keep the battery at full charge without charging it to death.
It’s probably shot due to sulfation which happens when a lead acid battery is left in a discharged condition for too long. Google “lead acid battery sulfation” for more on this topic.
Over the winter, you can leave the battery in the bike or remove it; your choice but you must use a maintainer/tender (approx $25) or a float charger (approx 10 or 15 bucks from Harbor Freight). I float charged one battery out of the bike and used a 1 amp maintainer/tender on the other battery left in the other bike last winter; both bikes started ok with no assistance from an external power source. Don’t use a charger continuously. If a charger is all that you have and can’t afford a maintainer/tender or a float charger, then charge your bike battery at least once per month for a couple of hours each time over the winter.
The post stating 30 minutes per day using a timer with a trickle charger should be ok too. A trickle charger is a charger, not a tender/maintainer nor is it a float charger.
The battery is ruined. Buy a battery maintainer/charger. It charges and then when capacity is reached it does not go into a trickle but shuts down and turns back on if the battery charge drops. It should come with alligator clips and a lead with rings on one end to attach it to the battery terminals. Pull the bike into the garage and simply plug in the charger to the lead that is attached to the battery.
In central IL the winter was horrible so I did not get the bike out except 2 times for 4 months. I would sometimes start it for maintenance but it always fired in a heartbeat.
You can put in on no problem. Anybody with a basic concept of “righty tighty, lefty loosey” can install the lead. Just keep it away from painted panels since the lead will flop around in the wind. I have mine nylon tied to the frame under the seat.