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Wet, Gel or AGM battery? Which One is Perfect for my Boat?

Wet batteries: the traditional ones

Over time, the “wet battery” with stoppers (screw caps) for refilling distilled water has constantly been evolving. Despite the many promising new developments, they are still far from being old – especially since their price-performance ratio is unbeatable. Compared to the closed design as it is today in the car standard, however, “open” batteries require some maintenance. The reason: During the charging process, hydrogen and oxygen are released, which escape through the ventilation opening. This reduces the level of distilled water in the battery and must be supplemented regularly. This means that the battery must be in an easily accessible location so that the water level control screws can be easily reached.
Maintenance is simplified by so-called “closed” (maintenance-free) batteries. In their cells, a water reservoir is installed, which is sufficient for three years of EU-standard car life. After that, the water level and thus its capacity begins to decrease accordingly until it slowly gives up its spirit. In case of doubt, “maintenance-free” does not mean “you do not have to wait” but “cannot wait.” This was only improved with the development of “sealed” batteries in which the battery cells are closed with pressure relief valves.

The cells of this new generation of power sources are hermetically sealed (welded), but equipped with pressure relief valves. However, the hydrogen and oxygen generated during charging cannot escape as in the “closed” wet batteries but is converted back to water by a side reaction (“recombination”). As a result, these batteries are completely maintenance-free – as long as the amount of hydrogen and oxygen produced during charging does not increase beyond the (limited) recombination capability of the battery. at

Deep Cycle Gel batteries

The battery fluid (the “electrolyte,” a mixture of sulfuric acid and water) is bound (“gelled”) by the addition of silica gel.

For this reason, deep cycle gel batteries are leak-proof and safe against sensing and can be stored much longer than standard batteries with liquid electrolytes. Because of the jelly-like consistency of the electrolyte, self-depletion is also significantly reduced – gel batteries survive well over nine months without recharging. For the same reason, gel batteries charge or discharge the flow of ions to the “wet battery” comparatively higher resistance. As a result, gel batteries are less able to deliver high currents in a short time. They are therefore not suitable for starting the engine but pure consumer batteries.

AGM batteries

(Absorbent Glass Mat) It is the most modern version of the lead-acid battery. In it, the electrolyte is bound in glass fiber fleece. This results in a low self-discharge, which makes recharging necessary only every six months if the battery is not stored above 20 ° C. AGM batteries, are also anti-tamper and leak-proof and can be installed in virtually any position, which is particularly beneficial on small boats.
Another advantage: in contrast to the gel, the fleece brakes the flow of ions much less. As a result, AGM batteries can be charged faster with higher power than gel batteries and lower internal resistance; they can, if necessary, deliver correspondingly larger amounts of electricity to the consumer. To Buy The Best AGM Battery, you should read our AGM buying guide.

Which one to choose?

If you want to recharge your battery with a normal alternator and a perhaps aged charger, if you find the effort of occasional acidity checks and eventually topping up distilled water reasonable, then wet batteries are still a proven and inexpensive choice. However, you should recharge these batteries at least every three months (winter storage).

If you need a battery that is completely stable, if you can not or will not recharge your batteries in winter storage, and you need the highest performance, then AGM batteries are your first choice.
Gel batteries are always the preferred type when exceptionally long storage times are required. You can also read the article AGM battery vs lead acid battery.

However, both types require a charge exclusively with an IU0U characteristic, which can only be achieved with a conventional alternator with a retrofit.

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