Lead-acid battery maintenance and diagnostics: What I have been doing

The stuff you learn as you go along ...
... needs to be shared with those that might not know yet.

When my Virago would not start two weekends ago, I and my friend jump-started it off his own bike. Once warm it would start again normally, so we set off for a 120 mile ride and I attributed the problem to myself: "I just flooded it when I first pushed "start" but now the alternator should get things in place again..." But that did not happen. Since then the bike did not start again without help, that is. It only fired up again with the help of the car's battery. I could jump-start it from the car, go for my ride and hope that it would start again (while warm).

Troubleshooting begins:

• Starter cranks the engine a bit (half-turns), neutral light fades while it happens
• The headlamp still works with the bike off

Seems obvious - it's a weak or half-dead battery.

Immediately I ordered a fancy charger (yes, it's blue! but in my defense, it was not my choice) to check and charge the battery, which failed miserably because it has not been delivered yet... Seems to be out of stock everywhere, I should have known better... Well, before the charger comes in, I figured I would do what I could to get more information out of the situation.

The exact model of the battery is Yuasa Yumicron YB12AL-A2. It's a lead-antimony type 12V 12Ah motorcycle battery. Yuasa kindly provide this very insightful document in their website summarising the technologies behind their ranges of batteries and how they fit into different types of requirements.

Before even taking it out, I noticed that no fluid could be seen around the MAX or MIN levels. Either because the plastic was too opaque or because the level was not even close to those levels. Next thing was measuring voltage levels in different situations: no load, loaded but engine not running, engine running. Results were approximately:

• Unloaded: ~13V
• Loaded: N/A (didn't measure)
• Running at idle: ~18V
• Running over idle, unloaded: ~17V

Aside from potential regulator/rectifier issues, I saw nothing particularly alarming here. So I took the battery out to have a good look at it. This visual inspection revealed the following:

1. All connectors and metallic contacts were in very good condition - no corrosion or grime even
2. The battery itself was clean and looks recent
3. There was no fluid whatsoever inside it. It was completely dry

All sorts of trouble may arise from semi-dry batteries, including quicker corrosion of internal and external materials due to increased acid concentration and electrical properties must change as well - from internal resistance, maximum current output, voltages, etc - nothing tolerable in the medium/long term.

What I cannot understand is how a completely dry battery could conduct *any* current, as it did. I would expect a battery to fail gradually before being completely dry which was not the case. A bit of misleading research led me to believe that this particular model of battery soaked the fluid (into some material) which would explain why it would not drip... True or false I don't know yet, as I could not find that information again. Oh, and there is also the little detail about: "Is the dry battery a cause or a symptom?" - I do not know yet.

If the battery was dead I would need to replace it. But it could also be brought back to life by filling it with de-ionised water and recharging. Having nothing to loose, I bought one liter of de-ionised water and (carefully) poured it in. [bloody filling holes must be made to be filled with seringes!!]

Immediately I measured a drop in voltage of about 1V. Back on the bike, I re-measured its voltage just to double-check that things were OK. Turned it on, re-checked things quickly, hit START and it fired-up promptly! Once more I measured voltages with the engine off and on, empty and loaded (lights on).

• Unloaded: ~12.1V
• Loaded: ~11.75V
• Running at idle, unloaded: ~17V
• Running at idle, loaded: ~13.5V (~15.5V when a little warmer, may go up a bit more)
• Running over idle, loaded or unloaded: ~16.5V

With the engine running, the electrical system should be mostly (or totally) powered by the alternator (stator/generator) through the regulator/rectifier, while at the same time recharging the battery for the next start-up (voltage at battery terminals should be >12V). This makes sense and my measurements are consistent. However, three things are still concerning me:

1. Loaded voltage is slightly below 12V and seems to drop quickly
2. Power coming from the charging system may have a higher than normal voltage (~17V)
3. According to manufacturer specs, 12.1V of unloaded voltage is equivalent to about 50% of charge

Best case scenario:

Battery is still good just needs maintenance. The least of my worries is buying a new battery.

Worst case scenario

Either the stator/generator or the regulator/rectifier (or both) systems are frying the battery. Not nice as the following might have to be replaced:

• Regulator rectifier
• Stator - Generator

While at it, why not read a bit more about the whole charging system. Knowledge is power.

• Wikipedia: Lead Acid Batteries article
• electrosport's How motorcycle chargins system works
• wemoto's Regulator Rectifier technical description and quick troubleshooting
• wemoto's Battery Care Guide
• Bit of theory with schematics and photos of regulator/rectifiers

Bye for now.