Low electrolyte levels - cause of flat batteries?

thor

Yesterday my car failed to start due to a flat battery so I took it out and charged it fully at home. Then I put it back in and the car started perfectly. So I left it at that and kept my fingers crossed it was just a one off. This morning the battery was flat again so I have come to the conclusion there must be something serious going wrong.
I am ruling out the alternator being unable to charge the battery because the car had not been driven and the battery should not go flat so quickly anyway.
There are so many other possible causes but there is one thing I noticed with the battery. The electrolyte levels seemed to be a bit low. They were not completely gone but were an inch or two from being full. Could this be a factor in batteries going flat quickly?

Joe_Horner

Low electrolyte can stop a battery holding a charge, but it can also cause other (permanent) damage if it's used or charged in that condition. The critical point is that the electrolyte should completely cover the plates in all cells - if it's below the plate tops then the first thing should be to top it up - use distilled water for preference but boiled and cooled should be ok if you're not in a very hard water area - and put the battery back on charge for a full charge again.

It'll either cure it or not but it's a lot cheaper than automatically replacing the battery

vaio

surely if distilled water is best then using boiled water (a concentrated solution of what is left when you distil water) is the worst thing to use.

wouldn't plain tap water be better? or maybe time to defrost the fridge/freezer?

Joe_Horner

No because boiling tends to drop mineral content out, (hence kettles furring up in hard water areas), and drives off the chlorine that's been added.

In practice, tap water is generally fine for the occasional top-up as long as you're not in a seriously hard water area but it's not the recommended way. Melted ice from defrosting a freezer is good but can be hard to collect now that all freezers seem to be auto defrosting.

Strider590

Ok, look...... Boiled water is no good, it needs to be distilled and/or de-ionised.
Water from a room dehumidifier is damn near perfect, pure ironing water is damn near perfect.

The purpose of the water is to act as a dilectric (or insulator), only pure water is going to be good enough.

forgotmyname

I got fed up of finding peas in the icei collected from the freezer. Not sure how they get there i never buy frozen peas.

Maybe they get free peas with every freezer?

I bo9ught 5L of the proper stuff from the supermarket whilst on offer.

Joe_Horner

Strider590 wrote: »

The purpose of the water is to act as a dilectric (or insulator), only pure water is going to be good enough.

No it isn't. The last thing you want inside a lead-acid cell is an insulator. the water and acid together form an electrolyte with a VERY low resistance (ie: exactly the opposite of an insulator, which has very HIGH resistance).

If the water acted as an insulator you'd never get any substantial current out of it because the internal resistance of the cells is in series with the load, so just 17 thousandths of an ohm resistance per cell would limit a 12v battery to 120Amps short circuit current, which is not enough to run many starter motors!

The reason that distilled water should be used is because the mineral content - mostly calcium carbonate (CaCO3) in hard tap water - interferes with the chemistry and damages the plates. Boiling and cooling precipitates the CaCO3 out, which is what furs up kettles.

mikey72

Strider590 wrote: »

Ok, look...... Boiled water is no good, it needs to be distilled and/or de-ionised.
Water from a room dehumidifier is damn near perfect, pure ironing water is damn near perfect.

The purpose of the water is to act as a dilectric (or insulator), only pure water is going to be good enough.

What's "ironing water"
Ours gets filled from the tap.

You're getting confused with dielectrics in things like capacitors that store a charge. Batteries have a solution of acid, electricity is generated by the chemical reaction. The water merely replaces that which is lost, and keeps the acid at the correct level. Any impurities like calcium in the water react with the acid, and can coat the plates, reducing the efficiency of the battery. Definately not an insulator in a battery.

Strider590

What's the point in arguing this sh*t? DONT USE TAP WATER IN ANY FORM!

Joe_Horner

Tap water is (usually) fine in practice for small top-ups. Currently have 2 cars with 6 volt electrics, both have batteries over 4 years old and both have been topped up with tap water several times over the past few years. Neither are showing signs of problems.

If you live on Salisbury Plain or near Dover, probably a bad idea to risk it but if you're in a soft water area there's no great risk - especially if the battery's possibly dead anyway!

mikey72

Strider590 wrote: »

What's the point in arguing this sh*t? DONT USE TAP WATER IN ANY FORM!

At least you've admitted you posted sh*t.
Joe had the right advice though.