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Your Alternate Battery Choice (the Gelled Electrolyte Battery)
By Tony Bingelis (originally published in EAA Sport Aviation, January 1992)
Many homebuilders who have used or are using a sealed immobilized electrolyte battery (a gelled cell type, that is) are quite vocal in their support or condemnation of these batteries. And yet, even those who do not think highly of them are most reluctant to change back to the old lead acid (wet cell) aircraft batteries.
That odd acceptance is enough to make anyone who has never used such a battery to wonder why. Let's see if we can't shed some light on the nature of the gelled cell battery that would justify such a less than enthusiastic acceptance.
What Is A Sealed Immobilized Electrolyte Battery?
What we homebuilders refer to, generically, as a "gel cell battery" is in reality leaning a bit on the registered trademark of the Globe Company's Gel/Cell© battery.
Technically, we are talking about "an immobilized electrolyte battery" (admittedly, a most cumbersome term) . . . in other words, a gelled electrolyte type of battery.
As I understand it, the gelled electrolyte technology was first developed in Germany some years ago. Since then, the concept of sealing an immobilized electrolyte in a case has led to the development and refinement of rechargeable maintenance-free batteries.
These sealed, non-spill batteries were found to be an ideal source for all kinds of portable power applications. The electronics industry is finding a myriad of uses for these sealed rechargeable batteries. These compact power sources have found wide acceptance for use in wheel chairs, portable test equipment and, yes, in aerobatic airplanes, too - so there must be plenty of good reasons for their growth in popularity.
The Gelled Type Battery's Better Features
1. The battery is constructed around a sealed immobilized (gelled) electrolyte which permits the battery to be installed and operated in any position. You could even install it upside down -but that would be kind of stupid. Unlike the liquid electrolyte found in lead acid wet cell batteries, there is no danger of the gelled electrolyte ever leaking out.
2. The typical sealed gelled cell battery is absolutely maintenance-free.
3. Obviously, this is THE battery to use in aerobatic aircraft . . . perhaps in most any homebuilt aircraft for that matter.
4. These batteries have a long shelf life. This minimizes the risk of buying a battery that has lost much of its capacity while on the dealer's shelf.
5. The average gelled electrolyte battery is compact and fairly light for its electrical capacity. Well, no heavier than a similar wet cell battery. For example, my present battery, a Sonnenschein (made in Germany), is a 12 volter with a 32AH capacity and weighs 22.5 lbs.
6. Regulations permit the shipment of these batteries by parcel post, UPS or by air without the need for special precautions or packing so they must be safe.
7. You can install this type of sealed battery in the cockpit area with no danger of suffering a corrosive acid spill or the presence of explosive gasses. For example, the Globe Gel/Cell battery features patented self-resealing vents which prevent high pressures from building during charging.
Incidentally, the first of the gelled cell batteries to become generally available to homebuilders was the Globe Gel/Cell battery . . . and that was not too many years ago.
I first saw one displayed in an EAA sales booth during an annual EAA Convention at Oshkosh and again later at a Sun 'n Fun Fly-In.
Since then these batteries have become a popular alternative to the old wet cell types. Their price is competitive, too (approximately $75 to $114).
As a result, the gelled batteries are becoming better known and more plentiful . . . they have not become cheaper, mind you, but are now much easier to locate.
For example, you can even order a gelled electrolyte type battery from your Sears catalog.
Naturally, not all gelled electrolyte batteries are alike, nor are all brands equal in capacity and reliability. You should be aware that most of these batteries were and are being manufactured for non-aircraft applications like standby power, communications equipment, golf carts and other high tech applications. It is not surprising, therefore, that some batteries may not have performed well in the more demanding aviation environment.
However, it is encouraging to note that aviation oriented manufacturers, including a few well known battery companies, are now producing or selling gelled electrolyte batteries for aircraft use under their own brand names.
The Battery's Physique
The gelled cell batteries used by homebuilders are fairly standardized as to size, weight and capacity This is important because . . . who wants a battery that won’t fit the location or battery box already installed?
The size of the typical 12 volt gelled electrolyte battery is approximately 7-3/4" long by 5-1/4" wide and 7-1/4" in height.
Weight averages range between 21 and 23 pounds for the 12 volt batteries.
Note: A variety of smaller, lighter, rechargeable gelled cell batteries are also available. These may be of particular interest to builders who fly homebuilts without electrical systems.
The "standard" 12 volt gelled cell battery has two "L" shaped terminals to which the battery cables are connected with 5/16" bolts using a lock washer and a plain nut. I prefer the use of wing nuts because they help control that homebuilder tendency to over-tighten everything . . . battery connections included. Battery post connections should be clean and tight but not so tight you twist the terminal post off.
The earlier standard sized batteries had a 28 amp/hour capacity but the currently favored unites now feature a 32 amp/hour capacity.
Construction of the battery and case is such that it is highly resistant to shock and vibration. The case is made of a non-conductive high impact plastic that will not deteriorate.
The battery is sealed and neither water nor electrolyte will ever have to be added. Indeed, your battery will be ready for use the minute that you receive it . . . and, happily , without first having to fill it with electrolyte, or to charge the thing.
Installing Your Gelled Electrolyte Battery
Absolutely no special preparations or requirements exist in this regard. A separate battery box is not essential although the battery can be better secured in one.
I am most familiar with the Globe Gel/Cell® battery as I have owned several of them through the years. The battery can be safely installed in a cockpit environment because it is sealed and its case is electrically non-conductive.
Note: The Globe battery folks do point out that care should be taken to ensure adequate ventilation . . . especially toward the end of a charging cycle and in the case of an overcharge. At these times, especially under an overcharge condition, hydrogen and oxygen gas is dissipated into the atmosphere. If allowed to accumulate in a confined area and a spark is introduced, an explosion might result. Therefore, some provision for ventilation and air circulation within the battery enclosure during recharge is advisable . . . I am sure this advice could apply as well to most other gelled electrolyte brands.
I can report, however, that I have never detected any fumes or battery odors from my gelled electrolyte battery installation in the RV-6. The battery is mounted up front . . . in the cockpit . . . in a metal case.
Although the battery case is far from being air tight, I would certainly remove the battery from the aircraft should it ever need to be completely recharged.
Before you try to install your battery in the aircraft, take the precaution of taping the terminal posts with masking tape to prevent inadvertent shorting against the aircraft structure or some nearby metal component.
After the battery is in place and secured, remove the tape from the plus (+) terminal and connect the positive cable to it first. Then connect the ground cable to the negative (-) post. The battery ground cable or grounding strap should be connected directly to the engine or to some heavier metal structure.
Double check and assure yourself that your connections are correctly made and that you didn't accidentally reverse the polarity by connecting the first cable to the wrong terminal post. This could damage your solid state gadgets when the master switch is turned on, and would undoubtedly blow your alternator diodes into oblivion.
Why Batteries Fail
I suppose most battery problems, with the exception of those resulting from old age, are aggravated by a poor installation and improper charging.
There is no reason why any aircraft battery cannot last 3 to 4 years . . .this includes the gelled electrolyte types, too. And yet I, like a number of other builders, have had my share of premature battery failures. I now wonder if all of the failures were the battery's fault.
I had one gelled electrolyte battery fail after 91 days. One did better than that. It only lasted 13 months. Another went 22 months before it started to ail. One was still going strong when I sold the airplane 3 years later. Either my electrical installation was improving or the batteries were getting better.
My current gelled cell battery is now 9 months old and is in excellent condition in spite of some heavy cranking and recharging last winter.
Friends and acquaintances tell of similar experiences. Past performance would indicate that some batteries (gelled types) last a long time while a few others fail completely in less than a year, or refuse to take and hold a charge.
It is difficult to sort out the reason or reasons for poor battery performance.
I know, for example, the 91 day wonder that failed was bought locally from a golf cart dealer. I suspect that particular battery had been on his shelf for a couple of years or more. As I recall, when the battery quit it would not hold a charge. I think, in this case, my voltage regulator was an accessory before and after the fact.
You can expect your idle battery to lose about 3% of its capacity per month at room temperature, and much more at 95-100 degrees F. I understand some idle batteries have been known to lose as much as 25% the first month.
I remember that one of my short lived batteries was one that I had mounted on the firewall in the engine compartment just about 6 inches away from the hot end of a large Cessna type muffler. I guess that one ultimately died of heat prostration, and the abuse it received from a poorly adjusted automotive voltage regulator that kept feeding the battery 14+ volts whether the battery needed it or not.
There is nothing wrong with using a properly adjusted automotive voltage regulator. They are inexpensive, light in weight, and simple to install. Furthermore, some of them are now solid state units and may even be temperature compensated.
Keep this in mind. The voltage regulator's sole duty is to keep the battery fit and happy. It should be installed near the battery in the same temperature environment. Neither the battery nor the voltage regulator likes a hot environment.
Keeping Your Battery Happy
My earlier battery systems did not include an over voltage regulator, hence the battery had no protection from an excessive charging rate that a faulty voltage regulator may sometimes impose on an already fully charged battery.
How the battery is being charged does affect its longevity and performance.
In this regard, an ammeter can help you keep tabs on your battery's condition. All you need to do is install a simple ammeter. One that reads - 30 - 0 - + 30, without other calibrations will do for a smaller automotive alternator. (Use a 60 - 0 - 60 gauge for a bigger 60 amp alternator.) Here's how to read your ammeter's behavior.
For example, your battery should reach its fully charged state within an hour after takeoff. On first starting the engine, the needle will show a high plus reading and gradually return to a slightly positive indication . . . if the battery, alternator and regulator are all working properly.
On the other hand, if after an hour of flying the ammeter needle still shows a heavy charge (+), your voltage regulator may be set too high, or you may have a bad cell in the battery.
Here's a third condition your ammeter can show you. Immediately after starting the engine, if the ammeter shows a much less than normal charge and begins to taper off even more, it is quite possible that your voltage regulator is set too low and the battery will never become fully charged. It could be, too, that your battery's internal resistance has increased to the point where the battery may be failing.
A second instrument can help you monitor your battery's condition and your electrical system. It is the voltmeter.
Gelled cell batteries do best when the voltage regulator is set for 13.8 volts.
This voltage setting can be verified with a handheld voltmeter or one you can install in the aircraft. It should be a good one. One that can be read to 0.1 volts.
One nice thing about a voltmeter in the instrument panel - as soon as the master switch is turned on, the gauge will show battery voltage.
With the engine not running, the battery voltage of your fully charged battery will probably be slightly below 12 volts.
Anyway, at a glance you can see if there is enough power in the battery to crank the engine. Of course, in flight the voltmeter should show the voltage output of your alternator.
Remember, your gel type battery likes 13.8 volts for a steady diet. If your voltage regulator drifts out of calibration and begins to put out higher voltage than that originally set, replace the regulator if it is one that cannot be adjusted or you will soon be replacing that battery and every other one that follows it.
The gelled electrolyte battery is a good one. Back it up with a good well adjusted regulator and an over voltage regulator and you will have the power you need when you need it.