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I use the same charger for my cars and bikes. If it won't take a charge it's probably shot. Most auto parts stores will check batteries for free.
 

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can a car 12 volt charger be used on a bike. i've been trickle charging a spare battery i have and 24 hours later it's only up to 9 volts.
The*rule of thumb is that you should never charge a battery at more than one-tenth its rating in amp hours. Meaning that a 20-amp battery should be charged at no more than 2 amps over a 10-hour period. Overcharging a battery can lead to all sort of problems: The electrolyte may boil, the battery can overheat and buckle the plates and, in extreme cases, the battery may even blow up, especially if excess hydrogen gas is released and there’s a spark handy. Large automotive-type battery chargers, designed to charge a good-sized car or truck battery, can easily overcharge a small motorcycle battery if you’re not careful. Unfortunately, in some circumstances, that may be the only type of charger available. Here’s the solution: Insert a standard test light, or even one built from a taillight bulb, inline between the positive side of the charger and your battery. Typically a test lamp, turn signal or brake light bulb draws about 2.25 amps. (If you’re not sure of the bulb’s amperage or wattage, hook an amp meter in series to measure the flow.) If you have something like a 6-amp charger that you want to use on your 20-amp battery, you’ll need to connect two bulbs in parallel. Yes, it’s a pain, but it’s better than cooking your*battery.

(From motorcyclecruiser.cim)

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Will the bike start? Bikes and cars are 12 volts but when charging a battery or starting a vehicle amps are really what's important. I normally try a quick charge first and then I see how the battery responds when connected to the vehicle. Is it a serviceable battery? If so I'd check the electrolyte level.
 

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not serviceable, sat on a shelf for two years hope it's still usable. with the charger hooked up the dash lights are dim and turning the key is no go. with the charger disconnected no lights come on at all. if i go for a ride tomorrow i'll put the old battery back in and the new one on the charger.it must take awhile to fully charge a battery.
 

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I've never used one that I knew had sat for that long but I've recharged some batteries over night successfully when my other bike had a short that would drain the battery.
 

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lead acid batteries have one nasty characteristic: when you use them (draw them down) you have to recharge them immediately

and I mean immediately.

That is how they work in a vehicle, you start the engine and take a lot of power out, and the alternator immediately charges the battery back up.

If a battery slowly goes dead over days or weeks, its usually shot after that. This is why you put a trickle charger (keeper) on your MC battery over the winter. Normally a battery will just stay charged for a few months by itself, but if its slowing draining down and you dont keep it charged, the chemistry on the lead plates turns into something else, and the battery will not recover.

Some people say you can put something in there (I dont remember what) and recover the battery after its been dead for a long time, but I dont know if that is true.
 

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Battery tender and a trickle charger not really the same. If thou have only 8 volts on a 12v battery, you either have 2 shorted cells or lots of sulfating. Writhe case the battery is probably toast.
One thing you can try is a battery tender, one that can desulfate by "exercising" the battery. They usually cost around $40-50. The process usually takes a week or so.

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$30 battery is usually not maintenance free. You can expect the cells to dry up easy enough. They normally only last a season or two, especially in a bike. Guess you get what you pay for. I've had my SGM battery three seasons. Cost more but never left me stranded.

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