12.5 would make a great voltage level for a battery SUBSTITUTION device.
We have to keep in mind, most most vehicles have flooded batteries that are maintained at 13.6 to 13.9 volts over most of their operational life. Doesn't sound impressive, does it. Now raise battery temperature to 140F
13.9? At 140F? Should remove all the water in what, say a week? A lot, meaning perhaps 99% of the utterly urban legend about 13.6-13.8 "boiling batteries" at moderate temperature is because...
The owner allows three months to pass. Checks his battery. Dry. Looks at the voltage (say 13.8) screams "Thirteen Point Eight Volts Boiled My Batteries Dry!"
Wrong!
The battery was OLD. Antimony migration. If enough plate antimony migrates to the negative plates, it increases electrolysis ONE THOUSAND PERCENT. Ten times the water usage of a new battery. It'll use TEN TIMES the water at 13.2 volts and TEN TIMES the water at 14.2 volts.
Get the picture?
Trying to share a complete picture that shows battery temperature and charging voltage involves too much typing. I can't do it. But at 0c 32F the "right" voltage is absolutely wrong for 30c 86F. Google BATTERY TEMPERATURE CORRECTION and look at the chart.
I have maintained a group 31 AGM Lifeline for almost 16 months now at 13.65. About four tenths of a volt higher float voltage than what Lifeline recommends. Of course they are correct. Of course my digital scale (after dust has been carefully wiped off the battery case, says the battery has not lost .01 GRAM of weight. When electrolysis occurs, a frees a hydrogen atom from the electrolyte, meaning two atoms of oxygen are liberated. FREE AT LAST. They don't stick around. One molecule of water says bye-bye. Water means weight. It ain't light. So you can bey your bippy one HUNDREDTH of ONE GRAM of water weighs less than one eyedropper drop. And guess what? The hundredth of a gram ain't lost.
The moral of the story.
Don't base assumptions, or conclusions about batteries by one single solitary experience with an episode that left you unhappy. Sure you found your battery smelling like Yellowstone National Park. Sure you found cells so low the plates were exposed. The voltage was found to be 13.8. Smoking Gun! WRONG! Old battery or memory fart. Yes the battery was checked. Just this last August.....2012
When a battery maintenance charger voltage is checked and it is of a reputable brand, it makes sense that this voltage is much more likely to be correct than the voltage of a product that costs one twentieth the price from a place that has a shaky (at best) reputation for electronics.
