What fluid is contained in this type of battery, and can it be topped up ? I have a supposedly maintenance free battery. Recently it has been running down unexpectedly. When I checked, I found most of the fluid was very low. What kind of fluid is this ? Plain distilled water or some kind of acid ? Advice appreciated
The same as in a normal battery: sulphuric acid, which should be fairly acidic when the battery is fully charged and more like water when it's flat.
Sulphuric acid but you usually top up with distilled water (or deionized water?) I suppose since the losses are due to evaporation and so what you've lost is water and not the sulphate ions.
Sulphates are lost too, as sulphur dioxide and trioxide. This is especially evident when the battery is in the erroneous state of being overcharged; the electrolyte is seething and bubbling in such a state, which in effect is an accelerated evaporation. These two gases form sulphurous acid and sulphuric acid respectively when dissolved in water, in normal as well as in accelerated evaporation. Herein is the rationale in the advice that the battery terminals need periodic cleaning with washing soda to neutralise the acid so formed around them (as white powder when dried) and protection with petroleum jelly.
The normal discharging and recharging cycles of an in-service modern battery, regardless of its being the regular, low-maintenance or maintenance-free variety, should lose little if appreciable at all of its electrolyte in its life time (nominally 4 years, but 10 years or more if well looked after): the amount lost is minimal. Do check that overcharging is not taking place, there is no engine overheating, or indeed the battery casing is intact.
Isn't the bubbling also hydrogen?
Yes, it sure is.
And I know from experience makes one almighty bang when coming in contact with any ignition source. It blew a hole in a door to the room it was in.
It's really disturbing to learn a story like this. It's not generally appreciated how powerful a hydrogen-air explosion is. Either there is no statistic available or the victims did not survive to tell the tale. The percentage of the lethal gas in an atmospheric air mixture is so tiny as to be almost negligible, and that's is why it's so dangerous -- only 4%. While it's true, hydrogen is very light, the moment it is liberated, it disperses fast, upward, but if the structure above is so fortuitously as forming an enclosed space thus an air pocket, then with an errant spark....bang. There goes another life or limb.
We are all grateful for your story.
The bubbling produces hydrogen and oxygen in the perfect proportions for an explosion. Hence a battery should never be charged in an enclosed space and extra care should be taken when connecting to or disconnecting a battery to not cause a spark.
That means never fitting one in the boot...
The message from "Dave Plowman (News)" contains these words:
Many batteries have a vent pipe nipple. All you need to is lead a bit of pipe from this through a grommet to the outside world.
Indeed. It's not charging in a confined space that is dangerous but creating a spark while the hydrogen is present. Used to be a regular occurrence when garages had battery charging rooms. These days H&S probably requires extraction to be provided.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.