Battery out gassing.

[Guest bill h]

I know Hydrogen is given off when charging. Is the situation similar when the battery is in use and providing energy? I know Hydrogen cannot be taken in when discharging but is there any gas presence localy when the battery is 'working'. bill h

[Clive]

Not normally - unless you short the battery terminals out then all sorts of nasty things happen including boiling electrolyte! Gassing increases during the later stages of charge, particularly if you want that last 20% in your battery and go for one of those charging systems that provide this. Gassing is the splitting of the water content of the electrolyte into hydrogen and oxygen in the perfect ratio to make a BANG if you light it! When the battery is getting towards fully charged the charging efficiency decreases as some of the amps split the water into gasses as above rather than revert the remaining sulphuric and lead contents into the charged state. This is why "advanced" charging systems only really apply to wet electrolyte batteries and why more frequent topping up with de-ionised water is required. On BIG battery systems as used on electric vehicles the batteries have automatic watering systems for regular topping up and special chargers to ensure they are fully charged. But that's a different ball game.