Absolutely dead battery? Battery been sitting for a while now it just wont turn your bike over? Charging system sucked your battery dry? Theres a chance you could save it, it only takes time and a couple bucks!
Make sure you're in a well ventilated area or outside on a breezy day. We're playing with various explosive gasses so its best they be dispersed
Get a big bucket, fill it halfway with hot water. Get a whole box of baking soda (family size, about 6 by 8 by 2) and dump the entire box in the water. Get a big stick and stir it around until its totally dissolved.
Pop the cell caps off the battery and set them aside. Using your big dishwashing gloves grab the battery and overturn it over the bucket, shake it up and down back and forth to get all the electrolye out and into the bucket. It'll either fizz or do nothing when the electrolyte hits the water.
Set the battery aside and stir the bucket around making sure to get the water up the sides of the inside of the bucket (gets all the acid off the walls of the bucket)
Now fill each cell of the battery up to the top fill line with distilled water. Make sure not to transfer any of the battery juices into the container of distilled water (via turkey baster/syringe). Its also important to note that you DO NOT want to contaminate the battery with the baking soda water, or the baking soda water with the distilled water in the container.
Leave the caps off the battery and hook the battery up to the strongest charger you can find. I use 'start' mode on my ancient roll around charger. It says it puts out 40 amps (somehow i doubt that). Make sure you hook the battery up first and then turn on the charger (trying to avoid sparks here)
I normally charge it at the highest, max smoke setting, for 20 minutes or so. Dont just time it, feel the battery on all sides with your hand (you did wipe the battery off didnt you). It will probably get warm, but when it gets hot (easily touchably hot but definitely towards the warm end of things) its time to stop. The battery will bubble during this process. Vapor will also come out of the cell ports. Nothing to worry about, just try not to concentrate it and breath it in (put your gold colored paper bags away!). The vapor is water vapor, hydrogen, oxygen, and sulpher dioxide (not 100 percent sure on the SiO2, but it is sulpher based).
Turn off the battery charger and unhook the battery. Overturn the battery over the baking soda bucket again, shaking it to get all the fluid out of the battery.
What most likely will happen at this point is the top part of the electrolyte will be inert, meaning no fizzing when it hits the water, but the bottom part of the electrolyte (thinking of the battery cell like a column of water here) will be quite energetic. Whats also likely is none of the fluid you dump out will be energetic, which means the battery is extremely sulphated, which just means things might take longer.
Repeat the above steps about five or six times. At this point the fluid coming out of the battery will at some point stop being so energetic. (Be warned this might end up taking ten times or so). This means that the sulphate is mostly gone and hopefully whats left is fresh plates, ie fresh battery.
Battery electrolyte is apparently hazmat now, so you'll have to take your battery to a battery store and have them fill it. I get mine filled for two bucks. (tell them you dropped your battery and it emptied itself or something, if you tell them what you're doing they'll probably laugh at you).
Put your battery on a slow charge (i do mine at 1 or 2 amps) for two or three hours. This will get the last of the sulphate freed up and also make sure things are operational. Check your battery voltage after this charge. It should be somewhere between 12 and 12.8 volts, possibly 13 if you charged it at a higher rate.
Put your cell caps back on, wipe off the exterior with the baking soda solution (dont get the solution in the battery!) and enjoy your fixed battery
[Caveats]
This wont work on ancient batteries. The plates themselves in the battery are physically destroyed. No amount of charging will put them back together again. Two years is right on the fuzzy line of being too old to try this on. Its cheap enough to try it on anything, but you might be wasting time with that 1985 vintage duracell. This process should work on shorted batteries as well, if the shorting is due to a sediment build up. Of course that sedimate is likely lead, which means your plates are destroyed which means you're wasting your time again.
Its obviously always cheaper time wise to buy a new battery, but rescuing an old one is recycling and better for the environment and better for your wallet. This method is for people with more time than money essentially.
__________________
