By Steve Krom
The most common killer of a wet cell battery is not using it. Ever wonder why the lawn mower or motorcycle won’t start in the spring , when you just bought the battery the spring before. The problem is simple chemistry. It’s called sulfation or sulfated plates. The battery is composed of a series of plates. Lead ( Pb ) is used for the anode plate ( – ) and lead oxide ( PbO2 ) for the cathode ( + ). The most common electrolyte is sulfuric acid, ( H2SO4 ). The amount of amperage in a given size battery volume is determined by the total surface area of plates in contact with the electrolyte. Note: that’s why the electrolyte level is important. For a given volume battery, lots of skinny plates means lots of surface area, hence a starting battery. Thicker plates in the same volume yields a deep cycle type.
As the battery is discharging, whether by running lights or sitting in the engine compartment, the lead plates are reacting with the electrolyte, making dc current and hydrogen gas. The sulfur is precipitating out of the electrolyte and onto the plates and the electrolyte is becoming more dilute, more watery. The amount of current draw is the only difference. When the alternator or other charging source is applied to the battery, this will convert and loosen the chemical bond of the sulfur to the lead plate, and put the sulfur back into solution, making the electrolyte more acidic.
Basically as the battery sits without being charged, the electrolyte is trying to go a neutral state. The longer the battery sits, the sulfur precipitates out more and more, the thickness of the lead sulfate, (PbSO3 ) gets thicker and thicker. Making it harder to be put back into solution. Also the acid electrolyte becomes closer to water density. Whether, it is a deep cycle or starting battery, as the surface area goes away, so does the amount of usable amperage. It will also give a false indication of charge level. You know the battery is down but your ammeter is not reading a very high output. Well your ammeter is indicating correctly. There is no place on the plates for current to go, thus no charging. The charging voltage is insufficient to break down the sulfate. This non reversible process takes on the order of months to achieve. The wet cell battery technology has been around along time. It does not occur overnight, am not trying to scare anyone.
For those who can’t decipher the verb-age, I’ll describe using a simple formula to illustrate the processes.
Pb + H2SO4 :::::: PbSO3 + H2O + 2e e indicates electron charge.
The ::::: indicates a parallel path
This formula goes in each direction.
Reading the formula from left to right.
The left side is the equation for a battery. Chemically speaking. If you are running lights or sitting there, the right side is the output of the battery. Hence the 2e indicates dc voltage. You can see how the sulfate is bonding to the plate material and the electrolyte is turning to water.
Now, if we reverse the equation and read it from right to left. The 2e part is the output of an alternator or battery charger. The result is the lead and sulfate separate and the electrolyte becomes sulfuric acid again. Time is not part of the equation, it does not become water overnight
Changing the electrolyte or using distilled water will not change the end result. You have a dead battery. Though, there is a way to possible bring it back. It will not be mentioned here due to dire circumstances of blowing up a battery, if performed incorrectly. This should only be left to competent pro’s with proper equipment and experience.
-Wet Cells or an AGM?-
AGMs are the best battery, right now, with the biggest bang for the buck. Lots of bucks though. The Optima battery is the most reasonable priced I have found. You get the amperage and cranking capacity in the frame size of a normal car battery. A wet cell battery of that ampacity, an 8-D, is the size of a small foot locker at 150 lbs.
AGM’s are also the most tolerant of being left unused. They can sit for longer periods and not lose any punch. They are less susceptible to sulfation. This is what makes them perfect for trailer rigs that might not see a lot of use.
AGMs have a high recovery rate of 40% of ampacity. A normal wet cells’ rate is only 25%. They means it takes less time to achieve full charge status. They are also best for letting stand for long periods of time without the need of keeping a charger on them. Though, it is always in your best interest to keep a charger on it, if the vehicle is not used on a routine basis. But be sure to hook it up at the first opportunity as we all know it’s easy to get to it later, days turn to weeks, weeks to months, months to a dead battery…..
They are a sealed battery and don’t require any maintenance other than charging. There is a vent built into the case for relieving built up pressures. But that will only occur if the charging source exceeds 15+ vdc.
The AGM likes to see 14.5V for charging and the typical vehicle alternator is close enough. I have not seen any problem with this voltage. Just ensure you have adequate ventilation around the battery. This is good advice for any battery style.
-Types of Chargers-
1. The most common is the automotive style. A ferro resonant type. Been around forever. It usually has a bulk and trickle charger. The bulk, as the name implies, a lot of current right now. The trickle feature allows the battery to charge slower at a lower voltage or maintain the battery state of charge to minimize sulfating. It is best to switch the unit to trickle after bulk to prevent over production of hydrogen gas, i.e. “ gassing off”. That is no reference to fred or joe p. either. If there is no trickle mode, put a timer on the charger. It can also deplete the amount of electrolyte in the battery, drying out the cells. These usually cannot select battery type and charging variables.
2. Another type becoming more affordable is the high frequency switching charger, also known as smart charger. It usually has three steps in its’ set up. Bulk, absorption and float. Float is nothing more than trickle. The charging and monitoring of the battery is hands free. These have settings for the various types. Wet, AGM, and so on. These can also be configured for multiple battery charging. You can charge up to three batteries at once. A bit on the expensive side. $200- $300 range.
3. The last to be mentioned here is the newest style. It is a pulse charger, as its’ name indicates it just sends a high frequency pulse into the battery at a preset times. This is supposed to keep the sulfate off the plates and not consume much power. Also it is smaller and less prone to overcharging the battery. they are more affordable. There are solar powered versions. I saw one with a cigarette lighter adapter. (Not sure about this one, sounds like a perpetual motion machine.) You power up a device to charge the battery that is powering the charger. This is just an opinion off of a picture of the unit. Have not read any specs on this one. I have not had an opportunity to play with these yet, but have read good articles on them
Any of these types are quality secondary charging for your battery. budget is the usual stipulation. In my experience, #2 type is well worth the money. There are single battery smart chargers on the market. Since I’m in the marine industry, multiple bank chargers are more common.
(Just for a little background, Steve is the electrician I go to before I mess up something electrical on my rig. He is one of the main electricians at the boatyard where we both work – Tony)
