Topping Up a Battery

Without doing any searching, plain old intuition tells me that it's not a good idea to pop the top off a battery while the engine is running. Last I checked, hydrogen gas is explosive. Probably not good to have everything energized.

Battery maintenance is usually done with the engine off. I would plan on buying a new battery. You have to wonder why only one cell would evaporate the electrolyte. This happened to a motorcycle battery and it would never fully charge after refilling the cell. Dealing with dying batteries is a pain, because it will fail to start at the most inopportune time. Hope the rest of your day goes better.

True.

To OP.

Always with engine off.

Batteries almost always fail one cell first, probably at least 99% of the time.....no matter what battery chemistry you are using......once one cell is weaker than the others, the other cells damage it further.....its a good sign to start looking for a replacement ASAP!

I always look for a battery that fits the space available in a car for example, sometimes a little taller, that gives me significant extra capacity. My Mitsubishi battery failed after 6 years this winter, it was 64 AH, I now have a 92AH battery. You notice the difference immediately.....old weak to new powerful!!!

There is slightly more risk when the engine is running, as the hydrogen gas is generated while the battery is charging. But unless the battery is significantly below full charge the risk is pretty low. I usually fill with the engine off more because any spilled water tends to drop into the radiator fan and splatter all over.

Off.

When the engine is running the battery is producing Hydrogen gas. It could go BOOM!

_{There's an echo here. I didn't see all the other corrct responses already given.}

Not quite true, gassing in a non sealed LA battery starts when the battery voltage exceeds about 13.2 volts or so (assuming that the battery is in a good condition and all cells are basically equal).

A battery with one bad cell may only gas from the bad cell for a long time before the other cells get a high enough charge to gas.....

A battery charged to 13.2 volts will have at best around only 70% of a full charge.....I use this fact on my caravan battery charger to a) stop gassing and b) to increase battery life dramatically......

You should never correct battery fluid levels while the battery is charging. If the battery is discharged you should only add fluid to those cells that the fluid level does not cover the plates. Only until it does cover the plates. The cells should be filled soon after being fully charged. The heat generated in the fluid causing expansion and the gases trapped in the plates during charge can cause the cells to over flow.

"The cells should be filled soon after being fully charged."

I believe this is wrong. The cells should be filled BEFORE charging.

At least wait until the battery has cooled.

That can damage any "low" cells as the charge is being forced through a smaller plate area....

Drying of plates will eventually cause the cell to fail first.

Always just cover plates and then charge....then check the acid density.

This come from experience acquired from 10 yrs servicing electro-motive equipment. Filling a cell before charging will some times cause the cell to over flow. As the heat generated expands the fluid and gases produced get trap in the plates displacing it.

I have found it best to correct just the cells where the plates are not covered. Adding just enough to cover them. Filling all the cells as soon as possible after the battery charge eliminates some of the possibility of over flow during future charges. As the fluid is still warm and expanded. There are some of the trapped gas are still in place.

ozzb I found out if you add eloctrolite to a cell before charging or running the engine the heat and expansion can spray battery acid on your motorcycle. I topped of the cells in a new battery. When I put the battery back in I kinked the vent tube. One of the cell caps blew off and sprayed the underside of the seat with acid. Fortunately this was noticed and washed off.

Just covering the plates is correct, more is unnecessary and can cause acid to be pushed out, possibly damaging the car.....better to check relatively often if the battery needs water regularly.....and remember that is an indication of possible over charging or simply the end of life of the battery.

A few years ago a car manufacturer had many cars that had to be taken off the road (some were less than a year old) due to acid damaging essential body parts, Renault I believe. Cheap batteries from Turkey that had been over filled was the reason.....I was unable to find a link about it though!!

I hope this helps.

I should have qualified my statement with; "fill the cells so the plates are covered". Overfilling the cells can cause it to overflow while charging. The point being; a plate that is exposed, will be damaged during charging.

Correct, overfilling can be bad news.

Sorry, but the rest of your comment is still not "correct enough".....

A partially exposed plate will only be damamged if the current used for charging is basically very high. Higher than most chargers will achieve, assuming for the moment say a car battery of around 50 AH......if only say 50% or less of the plate is covered you could be right......but that would be far more than we are talking about here to my mind....it would also either demonstrate a very weak cell or a weak owner!!!

The greatest danger to the plates is from drying out which will ruin that exposed area of plate completely.....that can happen without any charging being done.....

If I remember correctly, the air drying changes the chemical composition of the plate in some manner, perhaps someone knows the chemistry and can run it by us?

True, who wants an explosion! Beats me how just one cell could have evaporated electrolyte. Any way, the voltage now is less than 10V. Seems I need to replace the battery.

From my experience, If I top up a battery before charging, it will overflow sometimes. I expect the thing to do is just put in enough water to cover the plates, and then top it off after it is charged and cooled off.

Your failure is in "topping off". Just covering the plates is correct. Add no more than this, check at least once a month. When charging later, bubbles of gas form, displace acid and you get overflow.......you need lots of room for expansion....

A battery that uses water is either finished its lifespan, has a leak or is being overcharged too often......its a good indication of one of these bad conditions.....changes need to be made.

Too many people charge too much, beyond 70% shortens battery life, causes gassing and water loss. Its better to buy a battery with at least 30% more capacity and then only charge to 70%......70% is usually around 2.2 volts per cell. Check the manufacturers notes carefully....

Yup! It's best to top-up with distilled water before recharging.

If you top-up during charging you do stand the chance of having hydrogen gas being readily available for nasty things to happen.

During the charging process, the gas will normally be released and it is usually recommended that during fast charging that the caps be left off anyway.

During charging, there are usually hydrogen bubbles forming on the plates before rising to the top chamber above the plates.

This accumulation of bubbles increases the volume of the liquid/bubbles in the cell and therefore needs the normal air space available above the cells to cope with the greater volume. The liquid in the cell should then only be just above the plates before the charging process and should be maintained at this level during normal use (i.e. don't overfill).

If a cell has a significantly lower liquid level than the other cells, this is usually due to it producing more heat (and less electricity - harder cranking due to the lesser amperage produced) due to malfunctioning (shorting) within the cell.

Not much you can do in this case, but get a new battery and make sure that it is kept topped up.

Hey its been almost a day since topping up. Voltage is still around the 9V mark!

Hey, as per everyone else's remarks it's time to get that defective battery out of there or you may find yourself as the unlucky recipient of the next Darwin Award! Your battery has a shorted cell, as you keep trying to charge it the charging voltage is being distributed over 5 cells instead of 6. This results in an overvoltage and overcharging of the remaining cells, which in turn leads to them overheating and possibly buckling the plates. If the buckling occurs in the space above the electrolyte the sparking in the hydrogen rich atmosphere could easily result in the end of this thread.

You are right, but if it was ONLY Hydrogen as you said, it would not be a problem.

The problem is its actually an explosive mixture of Hydrogen & Oxygen.........

Correct, and as the battery undergoes charge/discharge cycles it "breathes" and draws in air/oxygen which mixes with the hydrogen.

From: http://www1.eere.energy.gov/hydrogenandfuelcells/tech_validation/pdfs/fcm01r0.pdf

"...Hydrogen is flammable over a very wide range of concentrations in air (4 - 75%) and it is explosive over a wide range of concentrations (15 - 59%) at standard atmospheric temperature..."

Actually a battery outdoors in free air poses very little risk due to hydrogen's buoyancy and rapid diffusion. The real danger is in enclosed spaces such as a battery room (or inside a battery casing) where the failure to properly ventilate the area can lead to dangerous concentrations of hydrogen/air.

The Oxygen & Hydrogen are both produced at the same time in a LA battery when gassing.

If I may remind you of water (a large part of the electrolyte in a LA Battery) is chemically H2O, which means that two parts of hydrogen are linked to one part of Oxygen to form water.....

Electrolysis breaks this bond producing 2 parts hydrogen to one part oxygen inside the battery, without sucking any air in. Sucking air in is unlikely while charging as a) the gases being produced will make a positive pressure in the battery, and b) the battery warms up when charging, will will also cause the gases inside to expand......

a) has the most effect once the battery starts to gas....

The mixture is called in Germany "Knallgas" which my dictionary says is "detonating gas; oxyhydrogen gas" in English!

'nuff said.

It is a good practice to check the battery electrolyte level,tyre pressure,engine oil level etc every morning before starting your vehicle.

Dear Mr. Mathewkyle,

Do not top-up while engine is running. Do it before starting the engine.

DHAYANANDHAN.S

I have from time to time topped my battery off using battery acid rather that water.

Is that an incorrect procedure of not?

Dear Mr. WAREAGLE,

You should not use ACID as top-up medium, for Battery.

In course of time, the water in the dilute acid will escape, by Evaporation as well as Chemical Reaction and ACID concentration will increase. This is DETRIMENTAL TO THE BATTERY.

I have experienced this.

THANKS,

DHAYANANDHAN.S

The comments so far have a few things that need addressing;
The battery producing 9V
Adding electrolytes
Bulging cells

Producing 9v -I presume it is a 12v battery. It should never be less than 11.5v. A 10.5v battery is junk. It would have 6x2v cells that would produce 12.54v (normal at a stable situation after being fully charged for a wet LA battery). A motorcycle battery may be a AGM type that doesn't require topping up and which has a slightly higher voltage.

These are general voltage ranges for six-cell lead-acid batteries:

• Open-circuit (quiescent) at full charge: 12.6 V (2.1V per cell)
• Open-circuit at full discharge: 11.7 V
• Loaded at full discharge: 10.5 V.
• Continuous-preservation (float) charging: 13.4 V for gelled electrolyte; 13.5 V for AGM (absorbed glass mat) and 13.9 V for flooded cells

1. All voltages are at 20 °C (68 °F), and must be adjusted −0.0235V/°C for temperature changes.
2. Float voltage recommendations vary, according to the manufacturer's recommendation.
3. Precise float voltage (±0.05 V) is critical to longevity; insufficient voltage (causes sulfation) is almost as detrimental as excessive voltage (causing corrosion and electrolyte loss)

• Typical (daily) charging: 14.2 V to 14.4 V (depending on temperature and manufacturer's recommendation!)
• Equalization charging (for flooded lead acids): 15 V for no more than 2.205 hours. Battery temperature must be absolutely monitored.
• Gassing threshold: 14.4 V

Adding electrolytes- During the charge/discharge process the battery plates change. Repeated discharges cause lead sulphate crystals to form on the plates and reduces the charging capacity. Just adding electrolytes doesn't change this buildup. It is possible to add a "rejuvinator" that will attempt to re-convert the crystals back to lead. This may help a little but in my opinion, if the battery has sulphation, it's better to get a new one.

Bulging cells- Step well back! If you notice a bulging cell, it doesn't mean it's going to explode immediately, but now is the time to retire it.

Dear all, Thanks for the input. I need to get a new battery. About 3 days now and we are still at 9V, no where near 12V mark.

Make sure to check every cell acid level,and make sure that all are at the same level as recommended by manufacturer.Many people distruct their devices just because they don't follow the operation & maintenance instructions provided by manufucturers.Auto electric guys say to top up distilled water when the engine is running,that means also the alternater is running.I don't have the technical reasons,let the forum help this!

DHAYANANDHAN

Thanks for the information.

Hey guess what? Just realized the voltmeter is faulty. Still indicates some 10V!