Thanks for the tips, guys. I'm going to try the fuse pull idea to see if I can isolate the problem, as well as get the battery tested.

I rode to work this morning and back this afternoon, with no starting issues. I am going to look in to it this weekend, and at least post a follow up if I find anything.

BobA, you missing a key factor in your calculation. Lead acid batteries can only use about 20-30% of there capacity before the voltage drops too low for electronics to function, and below about 60% of capacity they start taking damage.


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That's just not correct. Unless the electronics are extremely voltage sensitive or draw large amounts of current they will tend not to be affected much by the state of charge of the battery. Typically a lead acid battery will have an open circuit terminal voltage of around 12.6v when fully charged and around 11.7 volts when fully discharged (those number can vary very slightly depending on the exact construction of the battery). Very few electronic devices will care about the terminal voltage since most will be using a voltage regulator to stabilize the voltage somewhere between 5v and 9v. Voltage regulators are used because in normal operation the battery terminal voltage can fluctuate a lot, ranging from maybe 14.5v down to below 12v at times (and below 11v when starting). I'd guess the clock for example would continue to function all the way down to 95% discharge or more since it draws negligible current and probably only needs 5v.

As for damage, all lead acid batteries sulfate when discharged, but it's reversible as long as the battery doesn't sit too long in a highly discharged state. It's part of normal battery operation. It's certainly not true that below 60% charge a battery will suffer irreversible damage. However if you let a battery sit for weeks or months at a state of low charge, it will suffer irreversible damage. Even a few days at very low states of charge can do it. In fact if you never fully charge a battery and let it sit at a maximum 90% charge all its life, it won't ever perform as well as a battery that had been 100% charged whenever left to sit. How fast a battery will sulfate and at what level of charge is again related to the construction and design of the battery.

It is important to note though that lead acid batteries used in cars and bikes should always be stored at full charge if you want maximum battery life, that much is certainly true.

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Bob A.
Current bikes:
1990 Kawasaki Ninja 250 (Rebuilt)
2011 Suzuki DL650A

I've heard of some very dissatisfied owners of lithium batteries in MC's. They don't crank well at all in the cold. Some say you have to leave the headlights on for 10 min to get the battery warm for it to crank. Never had one...Just sayin.

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I believe this is incorrect. Deep discharging (50-60%) a lead acid battery reduces the life of the battery immediately. The more times this happens and/or the deeper the discharge, the shorter the life of the battery. If a battery is not of the deep cycle type this is even more true.

60% charge (i.e 40% discharge) isn't really deep discharge. Deep discharge batteries are designed to work with 50% to 80% discharge cycles.

Typically a car (or bike) battery is happiest with no more than a 20% discharge but a occasional 40% discharge followed by quick recharging to 100% charge, while not exactly good for the battery, probably isn't going to hurt it much.

As I said, the best condition for a car or bike battery is 100% charge and recharging to that point immediately after use. When everything is working well, the amount of charge used to start the engine will be quickly recovered by the charging system. When you're actually riding, the generator is providing the power, not the battery. The battery is in the circuit of course and acts to smooth out voltage variations and any spikes from the generator, but the generator is doing all the work. The only time the battery might be discharging (other than starting) is when the engine is idling (or off) and you have a lot of power draw (headlights plus turn signals plus brake light + accessories).

You will get maximum life from a battery if it's kept at 100% charge and never allowed to go below 10-20% discharge. Mild deeper discharges will slightly shorten the life but not by very much If you leave the bike with the lights on and the engine off and the battery fully discharges, then you have hurt it. Charge it back up right away and you'll probably be fine, but the life of the battery will have been shortened. If you leave it in that discharged state for days or weeks, it could kill the battery completely.

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Bob A.
Current bikes:
1990 Kawasaki Ninja 250 (Rebuilt)
2011 Suzuki DL650A