View Single Post
Old 06-09-2002, 02:46 AM
xs11 xs11 is offline
Super Moderator
Join Date: Jun 2002
Posts: 130
Post TLC for your motorcycle battery.

TLC for your motorcycle battery.
Stolen from the Airheads BMW Club newsletter - July 1995
TLC For Your Motorcycle Battery
by charter member Oak Okleshen #35
22637 S. Ridgeway
Richton Pk. IL 60047
Personal inquiries to Oak must include two first class stamps.


The subject of "How To" with motorcycle batteries has probably been beat to death dozens of times in past tech articles, and we may mutter "There ain't anything new we can learn about this mixture of lead, acid, and plastic". Taint so! Most of the damaging enigmas of batteries are not only passed by in the writings, but they are often contrarily understood. When you consider that the replacement cost of a battery is about a C note, careless treatment of your volts supply can be rough on the pocketbook.

This essay was prompted by a recent R75/6 battery failure. It was just 3 years old and well maintained. The battery had been properly prepped when new, and checked out as good as new only 3 months ago.


A battery is a living electro-chemical device and starts dying the day it is born, or more precisely, the minute it is activated from dry charge status. During the course of its use, it deteriorates gradually. Under the best of circumstances, will last approximately 5-7 years given optimum care.
What in particular damages the battery and limits its life?

1. Internal Heating

During the course of starting a vehicle, the starter draws tremendous current, in the vicinity of several hundred amperes. All batteries have internal electrical resistance. Some of the energy that is intended for external use (starting etc.) stays within the battery itself and produces internal heating. We know that the 12 1/2 to 13 volts at the battery drops to perhaps 9 volts under starting. Assuming 3 to 4 volts is dropped internally at a current of let's say 250 amperes, the internal heating power loss is approximately 3 1/2 times 250 or 875 watts. That is the same amount of heat produced in a good sized kitchen toaster. Excessive heat conditions produced internally are very damaging to the lead plates, the separators, and other internal structures within the battery. It can cause a certain amount of warpage and with it, loosening and loss of some of the plate material as it falls to the bottom of the cells. This in turn causes a loss of battery capacity, and additional internal heating in subsequent usage in a cumulative and increasing manner. Eventually, one or more of the 6 cells can short out, or lose enough capacity to cause total destruction. If one cell fails, the entire battery is ineffective.

Summer high heat conditions aggravate internal heat and can be the straw that breaks the camel's back. In the recent midwest heat wave, battery failures were so numerous that the subject made the front pages of the Chicago newspapers. Many stores were sold out of batteries!

2. Vibration

The motorcycle battery undergoes rougher vibrational treatment than its automotive counterpart. Vibration also causes plate material to dislodge from its support grid causing a loss of battery capacity which in turn aggravates the internal heating effect. The degree of vibrational damage depends on the motorcycle engine's vibrational level, and the road surfaces to which the motorcycle is subjected. Vibration is a highly variable factor in the determination of battery longevity.

3. Too Low a Battery Charge Level

Autos are generally used at frequent enough intervals and for long enough duration to keep the battery charged. The matter of a favorable charge level is somewhat of a tightrope act but is generally considered to be 95-98% of full capacity. Monitors to indicate their exact needs are not incorporated into charge systems as a study of cell electrolyte would be necessary. The charge needs are therefore based on calculated conjecture coupled with expected usage recycling. Voltage regulation is the extent of charge level control.

With motorcycle usage, the subject of battery charge can be a vexing problem. All batteries are subject to a natural self-discharge rate due to their inherent properties. Like marriages, they are not perfect, but beat whatever is in second place. The self-discharge rate is about 3 times greater in the heat of summer than in the cold of winter. Chemical reactions tend to revert to hibernatory status as temperatures drop, so while cold temperatures may cause batteries to lose capacity, they also reduce the rate of self-discharge.

If a rider lays his machine up in summer, self-discharge can take place in a matter of 3-6 weeks, especially if the battery was not fully charged before it was laid up. This can result in two battery detroying possibilities:

1. Internal overheating when starting is again attempted. Usually the starter will stall or nearly stall. With a stalled starter drawing high currents, severe heat damage occurs inside the battery.

2. Possible irreversible sulphation. If the charge level gets too low, the cells will undergo a partial to total chemical sulphation, depending on just how low the charge was. This kind of sulphation, with white crystalline deposits, is irreversible. The end result is partial to total loss of battery capacity and refusal of the battery to take a charge. Chemically, the battery has locked itself into a discharged condition. This kind of damage frequently occurs to folks who put their cars "up on blocks" before leaving for an extended trip, especially if it's over the course of a summer. The fix unfortunately, is a new battery.

The primary concern with cold weather storage, the kind everyone frets about in winter, is freezing of the electrolyte. But electrolyte freezing is not a concern in America if the charge level of the battery is 65% or greater. The best treatment for wintertime storage is to charge the battery to near full as possible, then keep it outside where it is cold. The very worst thing to do is take it inside and keep it warm and unattended next to the furnace. That will quickly cause it to develop the summer death syndrome.

4. Too High a Battery Charge Level

Yes, there are those who overcharge the battery. The usual belief is that during overcharge, the battery may lose some water which can then be easily replaced. Not so exactly. During overcharging, there is an abundance of oxygen gas released from the decomposition of water in the electrolyte. That passes through the cell areas and oxidizes the positive plates of the battery. This oxidation impairs the conduction of electricity and reduces the capacity of the battery.

5. Low Electrolyte Solution

This is usually an owner induced problem due to neglect and will subtract from battery longevity. It can also happen from long trips where the battery is continually fully charged and yet continues to charge, decomposing the water into hydrogen and oxygen gasses (called gassing). When the level of electrolyte drops, the upper part of the plates become inactive, further causing a reduction in total battery capacity. It also causes further heating due to an increase in internal resistance of the cells, and resulting heat damage.

I should mention that higher-voltage regulators (as some advertise) are not always a good idea. For short rides and commuting, maybe the higher voltage regulators make sense, but they do not see the higher voltage until the battery reaches a minimum charge level, so the reasoning justifying their use is superfluous to some extent. Batteries will charge just fine with as little as 13.5 volts applied to them, it just takes longer. BMW's standard voltage is 14.0 and it would be best to stick with that (using the standard regulator). Higher voltage regulators can easily cause additional water consumption and increased internal battery heating and result in the problems listed above.

6. Poisoned Electrolyte

Only distilled water should be used in the makeup of the electrolyte. One heavy dose of a high mineral content water can contaminate a battery and cut its life in half. High mineral content reduces battery electrolyte effectiveness as the minerals are foreign to the needed chemistry. Self discharge rates will increase along with sulphation and internal heating.

7. Overfilling the Electrolyte with Water

Clearly this is a man-made virus, as the temptation is to practice the theory that more is better. Absolutely not so. Overfilling causes two damaging problems:

1. During charging, gasses are generated within the electrolyte and will raise the level of the electrolyte , which is normal. But when it is too high by overfilling, the excess will spit out the vent, possibly causing corrosion on the motorcycle, and dilution of the electrolyte, which reduces battery capacity and causes excessive internal heating.

2. Overfilling can under extreme circumstances, also cause a liquid short circuit between each of the cells and create havoc with the heat so generated. This may destroy the battery and under some circumstances, cause it to explode with the high heat conditions generated.

So when they say don't overfill, they mean it. All that is really necessary is to insure that the top of the separators are covered with electrolyte. The level admittedly, is hard to observe. To ease that problem, shine a light through the battery from rear to front (bike on centerstand).