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I witnessed an impressive explosion of a lead acid battery when my collegue started an internal combustion engine connected with the battery without disconnecting the charger from the battery first.

What is the reason that charging the battery while using it caused its destructiion?

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    \$\begingroup\$ You can't physically discharge and charge a battery at the same time. Unlikely it had to do anything with the charger being still connected. You either got a steam or a hydrogen explosion, depending on what actually happened which is hard to tell without any information whatsoever \$\endgroup\$
    – PlasmaHH
    Commented Oct 16, 2017 at 12:23
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    \$\begingroup\$ Did he connect the charger the wrong way? \$\endgroup\$
    – user3528438
    Commented Oct 16, 2017 at 12:23
  • \$\begingroup\$ Almost anything will explode if you make enough current flow through it. In case of a lead-acid battery one only needs to make sure the electrolyte starts to boil. \$\endgroup\$
    – Bimpelrekkie
    Commented Oct 16, 2017 at 12:24
  • \$\begingroup\$ @user3528438 He just diden't unplug the charger. It was a battery of a merchant vessel engine \$\endgroup\$
    – veronika
    Commented Oct 16, 2017 at 12:26
  • \$\begingroup\$ @PlasmaHH Maybe charging while the battery was discharging increased the charging current \$\endgroup\$
    – veronika
    Commented Oct 16, 2017 at 12:29

5 Answers 5

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Overcharging the battery will result in electrolysis in the electrolyte (water and acid) and this creates hydrogen and oxygen.

If enough gas H2/O2 accumulates in the battery, then vents out from the internal pressure, when it comes into contact with a spark, it will explode.

Hydrogen is very flammable...

enter image description here

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  • \$\begingroup\$ Sorry same thoughts ... \$\endgroup\$
    – Solar Mike
    Commented Oct 16, 2017 at 12:29
  • \$\begingroup\$ No problem Mike ;) \$\endgroup\$
    – bobflux
    Commented Oct 16, 2017 at 12:32
  • \$\begingroup\$ ...but the Hindenburg was not overcharged, was it?!? \$\endgroup\$
    – Curd
    Commented Oct 16, 2017 at 13:04
  • \$\begingroup\$ the newest fad with the kids these days: zeppelin tuning \$\endgroup\$
    – Christian
    Commented Oct 16, 2017 at 13:21
  • \$\begingroup\$ Hindenburg was badly designed... \$\endgroup\$
    – Solar Mike
    Commented Oct 16, 2017 at 13:49
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Most likely it was not the charging or discharging that caused the battery to explode, it was the vibration caused by starting the engine that caused a spark which ignited the hydrogen gas being given off.

All too easy - seen it happen and had to save my mate by washing his eyes out - 3 cars needed to be re-sprayed...

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The battery was damaged, probably a shorted cell. At high current, let say starting current, but this can happen also at quick charge current, the electrolyte evaporated so quick, that formed a high pressure and exploded.

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My first guess would be that the battery electrolyte level was not checked BEFORE the charger was placed on the battery.

The electrolyte was below the top of the lead plates. The battery charger was placed on the end life cycle battery and generated (outgassed) large amounts of hydrogen and oxygen.

When the internal combustion engine was started the battery plates warped by the rapid electrical discharge draw from the electrical starter motor and NOT being submerged in electrolyte produced an electrical spark in a hydrogen / oxygen gas environment.

Hydrogen and Oxygen on an atomic weight basis; releases more energy than nitroglycerin .... BANG!

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  • \$\begingroup\$ Outside of boiling the electrolyte away in hydrogen / oxygen gas the continues battery charger exposed the pates and aggravated plate heat / chemical warpage. Had the battery charger been placed on a new life cycle lead acid battery the outgassing is not yet as severe as an older battery. And had the electrolyte level been checked and added (if needed) the continuous use of charger would be innocent of suspicion. Check the battery electrolyte before every anticipated starting or monthly. Keep a written record of levels added! \$\endgroup\$
    – Fred
    Commented Mar 8, 2020 at 15:28
  • \$\begingroup\$ Energy density of mixtures of Hydrogen and Oxygen is very low. And even less because air is mostly nitrogen. Use of atomic weight is misleading. Hydrogen density is so low it just floats away. \$\endgroup\$
    – david
    Commented May 17 at 2:56
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Experimental tests and direct experience have shown that overcharging in an enclosed environment tends to create a fairly even hydrogen distribution. If there is enough hydrogen concentration in the room to create an explosion hazard, the whole room goes up. (Note that hydrogen burns when the concentration is anywhere between "almost none" and "mostly")

The fact that this explosion was confined to the (boiling or sparking) battery, indicates that poor ventilation was not implicated in the event.

https://hysafe.info/uploads/papers/2019/270.pdf

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