a battery tender isnt a battery charger. Its not meant to charge a totally dead battery. If the tender doesnt go kaput it'll probably take a few days. Your battery's probably fine if its just 2 years old but i could be wrong. Places like advanced auto parts will test it for free.

I believe my trickle/float charger gives about 42+ hours to charge a battery that's at 20%. Put it on a full size charger overnight. I let my battery go flat twice and charged it back both times. When it quit this winter I went back with the same battery Yuasa YBL-14ah2, I belive. Maybe yours will come back.  

Usually not that long. Depends what the charge was. Assault and battery?  On the positive side, if you have the energy to see that the charge holds, you can rest assured the old crank will stew in some cells for a long time. On the negative side most charges like this just wont hold.... and I have no idea what in he** I'm saying. Sorry!

if the out put of the "charger" is 12 volts
it aint chargin its maintaining...
it takes 15 some volts to charge our 14 amp hour battery
plate sulfation and acid strenght are two factord that determine lenght of charge..

thumperclone wrote on 03/04/11 at 07:26:25:

In reality, if the output is only 12 volts, it won't charge, it won't maintain, it mite even run the battery down to 50% SOC
12.06 volt =50% SOC
But a battery will fully charge at about 13.4 volts, which is also the min voltage for maintaining (float charge) (all depending on temperature)
For many years 13.8 volts was the charging voltage for most lead acid batteries. In later years they found higher voltages (14-15v) not only charge faster, they also make batteries last longer by keeping the electrolyte  mixed better, and slows down sulfation. Some chargers have hi voltage desulfaters built in.