"proper" use of jumper cables

[xoxoxoBruce]

During the final stages of charging, all lead-acid batteries break down some of the electrolyte in a battery into hydrogen and oxygen. With sealed batteries, such as gel cells and AGMs, the gases are normally contained within the battery, although in certain circumstances (notably, persistent overcharging), enough internal pressure can build up to open pressure release valves and vent the gasses. With wet cell batteries – the type that need topping up from time to time – the gases are always vented.

Hydrogen, which is highly explosive, is much lighter than air, so typically will rapidly rise and disperse, so long as there is even minimal venting from the top of a battery box and from the top of the compartment in which the battery box is housed. However, if a pocket of gas forms, any spark (such as from a brushed electric motor kicking on) may set off the hydrogen, on occasion resulting in a powerful explosion. This is what blew the top off the Fukushima nuclear power plants in Japan. Occasionally, internal short circuits create a spark inside batteries that can set off a hydrogen explosion within the battery, blowing the case open. Note that this can occur with sealed batteries as well as with wet cell batteries.


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