Battery Comparison: Lead Acid, Gel and AGM

At the moment, there are three main types of storage batteries on the market: lead-acid with liquid electrolyte, gel and AGM. They all have the same principle of operation, but there are significant differences in the device. These differences give them special characteristics, however, each type has its own disadvantages that should be considered when choosing a battery.

Lead-acid batteries with liquid electrolyte

This type of rechargeable battery is the most widely used. Their design has remained largely unchanged since their invention in 1859.

The device and the principle of operation

There are six compartments or cans isolated from each other in the battery case. Each compartment contains lead plates and a liquid electrolyte. Plates with positive and negative charges (cathode and anode). Lead plates may contain impurities of antimony or silicon. The electrolyte is a mixture of sulfuric acid (35%) and distilled water (65%). Between the lead plates are porous spacer plates called separators. They are necessary to prevent short circuits. Each bank produces about 2V for a total of 12V (daisy chain).

The current in lead acid batteries is generated by an electrochemical reaction between lead dioxide and sulfuric acid. This consumes sulfuric acid, which decomposes. The density of the electrolyte decreases. When charging from a charger or from a car generator, the reverse process (charging) occurs.

Advantages and disadvantages

The widespread use of lead-acid batteries is facilitated by their simple and reliable design. They give out rather high starting currents for starting the engine (up to 500A), they work stably up to 3-5 years with proper operation. The battery can be charged with increased currents. This will not harm the capacity of the battery. The main advantage is the affordable price.

The main disadvantages of this type of battery are associated with maintenance and operation. The electrolyte is liquid. Therefore, there is a danger of its flow. Sulfuric acid is a very corrosive liquid. Also, corrosive gases are emitted during operation. This means that the battery cannot be installed inside the vehicle, only under the hood.

The driver should periodically monitor the battery charge level and electrolyte density. If the battery is recharged, it boils. The water evaporates and needs to be refilled periodically into the compartments. Only distilled water is used.

The charge level must not be allowed to drop below 50%. A full discharge is guaranteed to destroy the device, as deep sulfation of the plates occurs (formation of lead sulfate).

It is necessary to store and operate the battery in a strict vertical position so that the electrolyte does not leak out and the plates do not close together. Shorting can also occur as a result of the plates crumbling.

In the cold season, the battery is usually removed from the car so that it does not freeze. This can happen with liquid electrolyte. A cold battery also works worse.

Gel batteries

Gel batteries work on the same principles as conventional lead-acid batteries. Only the electrolyte inside is not in a liquid, but in a gel state. This was achieved by adding silica gel containing silicon. Silica gel keeps the electrolyte inside. It separates positive and negative plates, i.e. serves as a separator. For the manufacture of plates, only highly purified lead is used without any impurities. The dense arrangement of plates and silica gel provides low resistance, and therefore fast charge and high recoil currents (800-1000A per starter at start-up).

The presence of silica gel also gives one big advantage - the battery is not afraid of deep discharges.

The sulfation process in such batteries is slower. The resulting gases remain inside. If too intense gas formation occurs, excess gases escape through special valves. This is bad for battery capacity, but not critical. You don't need to top up anything. Gel batteries are maintenance-free.

Advantages and disadvantages

There are more pluses of gel batteries than minuses. Due to the fact that the electrolyte inside is in a gel state, the battery can be safely operated in almost any position and place. Nothing spills like it can with liquid electrolyte. Even if the case is damaged, the capacity of the battery is not reduced.

The service life of a gel battery with proper care is about 10-14 years. Since the sulfation process is slow, the plates do not crumble, and such a battery can be stored for up to 3 years without recharging and with a large loss of capacity. It usually takes 15-20% of the charge per year.

The gel battery can withstand up to 400 full discharges. This is again achieved due to the state of the electrolyte. The charge level recovers quickly.

Low resistance allows high inrush currents to be delivered, ensuring high operating efficiency.

The disadvantages include sensitivity to overcharging and short circuits. Therefore, such batteries indicate the permissible voltage parameters during charging. You also need to charge with a voltage of 10% of the battery capacity. Even a slight overvoltage can lead to its failure. Therefore, it is recommended to use special chargers with such batteries.

In extreme frost, silica gel can also freeze and lose in the container. Although gel batteries withstand frost better than conventional batteries.

One of the main disadvantages is also the high cost of gel batteries in comparison with simple ones.

AGM batteries

The principle of operation of AGM batteries is the same as for the two previous types. The main difference is in the design of the separators and the state of the electrolyte. Between the lead plates is fiberglass, which is impregnated with electrolyte. AGM stands for Absorbed Glass Mat or Absorbed Glass Fiber. For the plates, only pure lead is also used.

Fiberglass and plates are pressed tightly together. The electrolyte is retained by the porosity of the material. A low resistance is created which affects the charging speed and the high kick-off current.

Such batteries are also classified as maintenance-free batteries. Sulfation is slow, the plates do not crumble. The electrolyte does not flow and practically does not evaporate. Excess gases escape through special valves.

Another feature of AGM batteries is the ability to twist the plates into rolls or spirals. Each compartment is in the shape of a cylinder. This increases the interaction area and improves vibration resistance. Batteries in this design can be seen from the well-known OPTIMA brand.

Advantages and disadvantages

AGM batteries can be operated and stored in any location. The body is sealed. You only need to monitor the charge level and the condition of the terminals. The device can be stored for 3 years, while losing only 15-20% of the charge per year.

Such batteries give high starting currents up to 1000A. This is several times higher than usual.

Full discharges are not scary. The battery can withstand 200 zero discharges, up to 500 half discharges and 1000 discharges at 30%.

AGM batteries perform best at low temperatures. Even in severe frost, the characteristics do not decrease. They also tolerate high temperatures up to 60-70 ° C.

Like gel batteries, AGMs are sensitive to charging. A slight overcurrent will damage the battery. Above 15V is already critical. Also, a short circuit must not be allowed. Therefore, you should always use a dedicated charger.

AGM batteries cost several times more than conventional ones, even more expensive than gel ones.

Conclusions

Even with such significant advantages, gel and AGM batteries could not squeeze lead-acid batteries. The latter are more affordable and do their job well in a car. Even in the cold season, 350-400A is enough for the starter to start the engine.

On a car, AGM or gel batteries will only be relevant if there are a large number of energy-consuming consumers. Therefore, they have found wider application as energy storage devices from solar panels, wind farms, in homes or as a source of energy and in various portable devices.