As I work with industrial batteries everyday, maintenance is sort of ingrained in my job description.
This thread pertains to the maintenance requirements and procedure for a flooded battery such as those that are installed as original equipment in my KLR, but it will apply to any lead-acid battery.
First a little technical info on how the flooded, or wet cell battery works:
The battery body is typically molded out of acid-resistant polycarbonate plastic. There are 6 individual cells molded into the body and lead plates are then inserted into each cell. The plates are immersed in a solution of sulphuric acid that acts as an electrolyte
for the charging process. I could go into more detail on the charging/discharging process, but it isn't really pertinent for this particular thread.
Each cell has a charged capacity of roughly 2 volts, thus a 6 cell battery equals 12 volts of electromotive force at varying rates of amperage depending on the battery's construction. This charged capacity changes throughout the cyclic life of the battery and can yield a very wide range of total battery voltage from typically 11.0 VDC up to a safe maximum of 14.4 VDC. The available battery voltage and power is dependent on how often the battery is discharged and at what rate. There is a whole slew of mathematical equations to calculate this, but I won't go into those here.
Now we get down to the nitty-gritty of battery maintenance for the wet cell, or flooded battery.
Remember I said that the battery is molded with six individual cells? Well, those cells are not shared with each other until the electrolyte flows over the top of the cell wall. Picture the bulkheads from that Titanic movie where the water spilled over the top of each wall and created a new "cell" of water. The problem with this type of battery construction is in the way some batteries are positioned in the bike. You may be given the false sense of security that your battery is filled to it's proper level and at maximum operating voltage by looking at only one side of the battery's body through an opening in the tray. If you were to actually pull the battery out of it's tray, you might notice that one or more cells are way below their minimum capacity of electrolyte. This important tidbit of information cannot be seen by simply glancing at the battery side while installed.
In order to bring each cell back to it's proper level of charge and electrolyte capacity, you need to do a little maintenance work.
Check the top of the battery terminals and each cell cover for sulfated acid buildup. It will look like a chalky residue sometimes green or white. If you see this, clean it off with a solution of 3 parts baking soda to 1 part distilled water to neutralize the acid from burning your fingers or corroding your tools. You can also purchase a spray terminal cleaning solution from any auto parts store that neutralizes the acid buildup. It changes color from yellow to pink as the acid is neutralized.
Now that you have that done, disconnect the battery cables from their terminals by removing the negative terminal screw first, followed by the positive. Why, you may ask? The negative terminal of a battery is the grounded terminal, and connects the entire chassis of the bike to the battery.
With the cables safely disconnected and out of the way, remove the overflow tube from the side and remove the single screw that holds the tray assembly together. Gently slide the battery towards you and always hold it by the bottom.
Set the battery on a stable, clean work surface with plenty of light so that you can check each cell for proper electrolyte level. You should see two lines on the face of the battery for a minimum and maximum level. If you notice any cell below the minimum level, you will need to top off the battery and bring it back to its optimum charge.
Before removing the cell caps and topping off, clean the top of the battery with a washcloth a solution of warm soapy water or something like diluted Simple Green. This will prevent any debris from entering the cells and interfering with the correct charge of the battery.
After the top is cleaned, don some good rubber gloves and gently remove each cell cap with a pair of small pliers. Be careful not to pull too hard or it may splash a little acid.
You should only top off the battery cells with distilled water or a pre-made electrolyte solution. You can usually buy the solution at any auto parts store, but distilled water is much, much cheaper and less dangerous to handle/store.
Using a funnel, fill each battery cell to a mid-point between the min and max lines on the battery face. It is not wise to fill all the way to the maximum line, as the electrolyte can boil under heat and cause an overflow.
After topping off each cell, connect the battery terminals to a trickle charger that delivers 2 amps. This will ensure a complete and ideal charge for the entire battery. Quick charges are not recommended unless you are under a considerable time constraint. Quick charge at high amperage rates may not adequately charge each cell and the battery life could be considerably shortened. Do not simply re-install the battery after topping it off in the hopes that the KLR's charging system will bring the battery back to its optimum level. The bike's system is not designed for this task. It is best to use an external charger designed to deliver a controlled level of amperage over an extended time period.
When the battery is fully charged and topped off with electrolyte, re-install making sure to connect the negative terminal last. Adding a dab of dielectric grease to each terminal when connecting will help yield the maximum amount of cranking power the battery can deliver.
I recommend checking your battery cells at least every other oil change and more often if you ride in a region of high heat. I hope this helps some of you that, like me, still use the flooded lead-acid battery.
There are better, and safer, battery designs out there such as Gel Cell and AGM (Absorbed Glass Mat). They are more expensive, but utilize a safer medium of electrolyte that cannot spill. The Gel cell uses a silica additive that causes the electrolyte to become stiff and immobile. AGM batteries are still considered a wet-cell battery, as the gal is absorbed into a weaved glass mat, but is still a wet gel.