Lead acid battery boiling during charging: this is bad, right

automotivebattery-charginglead-acid

I'm an electrical engineer who could use some help understanding lead acid batteries.

I recently bought an old motorcycle and charged the battery on my trusty automotive style battery charger after it lost charge. After several hours, the water was boiling inside the battery. I'm fairly certain the battery is relatively new and the water level was correct the last time I checked. I didn't have my multimeter at the time so I didn't take any measurements, but the battery is 12V and charger was set to 10A.

  1. Is it normal for the water to be boiling?
  2. Is my charging current set too high?
  3. Can permanent damage result from boiling?
  4. Is this the reason they must be topped off with water from time to time?

Thanks!

Best Answer

  1. Yes it is normal for the water to boil if you are overcharging it, with a too high current. And it is bad.
  2. Yes your charging current is set too high. Also check that the final float voltage from your auto charger is correct to the final charging voltage of your battery.

From Yuasa batteries (pdf): yuasa techmanual

For the correct charge rate a rule of thumb is to divide the battery’s amp hour rating by 10. For example a 14 AH battery should be charged at 1.4 amps (14AH÷ 10 = 1.4 amps). See the section on “Choosing a Battery Charger” for
more details.

When charging amperage exceeds the level of the natural absorption rate, the battery may overheat, causing the electrolyte solution to bubble creating flammable hydrogen gas. Hydrogen gas, when combined with oxygen from the air, is highly explosive and can easily be ignited by a spark.

  1. Yes.
  2. You shouldn't boil them. But some evaporation will still occur. Even "sealed" batteries have a safety valve for venting if they are overcharged.
Related Topic