can a battery tenders charge a dead battery or are they only for maintaining charges? i havent played with the 250 ninja in a while and when i was warming up the bike the bike died and wouldnt start again...not even a sound from the starter...just nothing....my gs battery died the same way, when it was warming up...but the starter did make a sound when i tried to start it....ANYWAYS
since in gonna need a tender for the ninja anyway, will it charge a dead battery?  thanks.

charge it for a good eight hours and see. I think it depends on how far gone it is.

If the battery voltage has dropped below 10V it is stuffed and should be replaced.  

Also depending on how your trickle charger works it may or may not be able to bring the battery up to charge.  A smart charger (microprocessor controlled) like Battery Fighter is always best for charging and maintaining a battery.  A lot of trickle chargers can damage a battery as they are more often designed for use in alarm systems and the like for topping up their battery backup systems and not long term storage of bike batteries.

This link is of interest to anyone who is installing a new battery - basically don't use the battery straight away and always give it a charge before 1st use to get the most of of the battery:
    http://www.docnsw.org.au/articles_jan02_firstfeed2.htm

Cheers
Conrad

i usually use a 2ampere auto batt charger, and my voltmeter to charge. i dont have a battery tender as of yet

is "battery tender" the best or do they charge a premium b/c they are the most well known? the yuasa hot shot is a charger-maintainer that has msrp of $30...almost half the price of a battery tender

Over the winter when my batteries are off-bike, I charge them once a month for about 8-10 hours with a NAPA 4-amp charger.  I've never had a problem with this procedure.  The Yuasa website does have a lot of good battery information.  www.yuasabatteries.com

Our local shop has Battery Tender brand ones for $21 on the shelf.

that probably a battery tender jr...whats the diff btwn those and the battery tender plus anyways?

BUT...do batteries tenders charge batteries or merely maintain them?

It depends on the condition of your battery (how much it is discharged), and it depends on the battery tender or trickle charger. I would think on a good battery that is completely discharged, yes, because electricity is still being passed to the battery, no matter how low the amperage. But it will take a long time. If the trickle charger has an automatic cutoff, then leave it for a couple of days.

I have heard of the rumor, that batteries have a "memory" of how they are charged. If you charge them slowly, they'll discharge slowly.

In order to "top-up" or maintain the battery, the Battery Tender needs to be supplying > 14v (any amperage).  Given enough time, it could charge a completely new (uncharged) battery.  How much time?  Rough estimate is that, if the battery is 11 amp-hours (11Ah), then in a perfect world, the battery would run for 11 hours supplying 1 ampre, then it would suddenly be completely flat; and it would take a 1 amp charger 11 hours to fully charge the battery.  Sadly, we don't live in such a world, so the battery will be flat long before 11 hours, and will take more than 11 hours to charge... but the basic idea is that, if the voltage being supplied is at the battery's gassing voltage (14 to 14.4v), then the battery will eventually reach full charge.  The amperage helps determine the speed of the charge cycle.  A smart charger will start with more amps, then taper-off to a trickle as the battery nears full charge to prevent undue gassing and heat.

Some causes of failure in lead-acid batteries are running completely flat, which causes active material to drop off the plates onto the bottom of the cells, eventually shorting a cell; and overcharging; and to a smaller extent discharging or charging too fast (generates heat in the cells, and the plates can warp, and eventually some of them touch and short a cell, reducing the effective size of the battery). Car alternators will try to charge the begeezus out of a battery, and contribute to this problem.  

I've never heard of a problem with charging a battery too slow.  Slow is good.  A battery tender should be nice and slow, assuming you've got the time to wait.   If it's rated at 1 amp, that should be plenty fast.