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I have in other forums had disussions regarding Gel versus AGM - I recommend you buy AGM which is is completely different, but GEL is probably better than standard lead acid in my opinion - Gel are good in my experience for starting every day and still not as good as AGM if they are not run every day.

They do not compete with AGM type when you look at the benefits. Below is an explanation on why an AGM... might be the most suitable for Jet ski's which are not started every day like your car... similar to boats and RV's.

AGM (Absorbed Glass Matt) batteries have huge advantages over conventional batteries in most circumstances.

For most people, people AGM (Absorbed Glass Matt) batteries will have a huge advantage over the conventional wet cell battery.

Although this will get a little long winded, it’s well worth understanding the virtues of both types of batteries, and how you can put them to best use, I won’t go deeply into the technical details of these batteries, just point out some of their advantages, and why.

Basically it starts with how you intend to recharge your batteries, I am talking about your main recharging source here.

If you are going to be using any of the smart charging solutions, like solar panels and a quality smart regulator, or a smart 3 stage mains (240v) battery charger, or the Christie Honda petrol charger (set to hi charge), then in most cases the conventional wet cell battery will serve you well. In our jet skis this is NOT the case..

If treated correctly (and few are) conventional batteries can outlast AGM’s, but only if they are well maintained and cycled within their design perimeters, with both correct discharging/charging and equalizing (now that a whole other story) and with keeping electrolyte (water) levels up.

However if your main source of charging is from your vehicles alternator, like in a jet ski, or you need to place the batteries in places that are less than optimum for safe battery storage, keeping in mind that wet cell batteries give of hydrogen (explosive) gas as they are charging, then you should consider using AGM batteries as they are totally sealed and spill proof.

A bit about Alternators.
Standard car and truck alternators are designed, for various good reasons to recharge car batteries to only 70-80%, and this works very well for normal cars and trucks being used EVERY DAY, but when it comes to charging wet cell batteries, where of course we need as full a charge as possible, that same 70-80% is not very helpful at all.

Float charging helps but still is not ideal.

All Automotive battery chargers suffer from much the same less than perfect regulation as car alternators, and achieve much the same results, and take a much much longer time to do it.

As an example lets imagine you have a 100 A/H(Amp Hour) battery, and you main charging source is you vehicles alternator or a standard automotive battery charger, now both of these will only charge this battery to about 75% (75 A/H), and you should not discharge your batteries below 50% (50 A/H in this case) of their capacity (see note below) if you want them to last, so all you can really safely use of this 100 A/H battery is 25 A/H, not much eh?

All conventional wet cell battery manufacturers say that their batteries are designed to be cycled to 50% of their rated capacity!

So each and every time you take these batteries below this 50% you are shortening their lives, and if you do it regularly and deeply you will even more dramatically reduce their lives.

Now remember the 100 A/H battery with only 25 A/H usable? A huge gain can be had if you are using any of the smart charging solutions, like solar panels and a quality smart regulator, or a smart 3 stage mains (240v) battery charger, or the Christie Honda petrol charger (set to hi charge), you can expect close to 100% (100 A/H) charge,
So 100 A/H capacity, discharge to 50% (50 A/H), that’s now 50 A/H usable, twice what you had before!

Now lets look at some of the direct advantages of these AGM batteries.

These batteries are totally sealed, ‘transport’ classed as spill proof, never needing topping up with water, ever! because of this they can be mounted inside a car, caravan, motor home etc and only need to be vented to atmosphere, they do not need to be in a sealed box vented to the outside like wet batteries, and can be mounted on their sides or ends if needed.

Because of their very low internal resistance these batteries will fully charge at a lower voltage, and accept a much larger charge current, so when charging from a standard car/truck alternator these batteries will all but fully charge, and fast too, in about 2.5 to 3 hours!

They can be discharged much much deeper than conventional deep cycles without major damage.

These batteries when left unattended only self discharge at the rate of up to 3% per month, and even after 12 months sitting idle can be recharged and put back into full service without any ill effects. PERFECT FOR JET SKI's. On the other hand a standard wet cycle battery if treated the same way will have destroyed it's self, it will no longer hold a good charge, and is sadly ready for the rubbish tip and recycling, not cycling!

AGM batteries were originally developed for the military, they are very robust and will take a real pounding.

The original AGM batteries were made in the US, brands like Odyssey, Concord, Lifeline, all excellent batteries, used extensively also in the aircraft and in the motor racing fields, but hugely expensive, there are now a lot of these (AGM) types of batteries coming out of China, and some are just rubbish.

My battery dealer's battery supplier (ALCO Battery Sales Australia) has found a couple of company's over in China that has been in production for many years, and have been selling batteries into the European market for a long time and have built up very good reputations, ALCO now import these batteries into Australia and are selling them through their own outlets and dealers like the one I buy from. The batteries are branded Fullriver and ALCO.

I currently have a 120 Amp Hour in my boat, I have a 90 AMP hour AGM in my Landcruiser which works in very hot conditions, I have one that runs a 12Volt Fridge on week ends away and a couple of others around the place and all still give me perfect performance and one in my Jet ski(just put that one(20 Amp Hour) in 18 months ago)

These AGM valve regulated batteries (also called SLA or Sealed Lead Acid) offer very good value, and when compared to standard deep cycle batteries in a dollar per usable amp hour format, they come out miles ahead, plus all the added advantages that I have already outlined, plus more.

I learned that in a jet ski - if you have a faulty wet cell standard battery, if it develops a fault, it can spew acid up the vent pipe and permanently damage your paintwork. Also, When they die, they just DIE - usually very little warning - I used to start my jet ski for 5 seconds before leaving home to check the battery - Even though I did this - one day when I got on the water at the ramp and tried to start it - it was dead yet 30 minutes before hand it was fine.. also, if you do deeply discharge a standard wet cell battery, just charging it with your alternator could get you into trouble - you stop at a beach after 30 minute of running and go to start again and find it just hasn't got enough to start - this is because the batteries often wont accept a high amperage especially if discharged a lot - AGM accept much higher charge rates and "fill up" faster.

Please note, my comments in this article are for batteries that are to be used in recreational vehicles, boats etc, and are used for weekends away and a few months a year, AGM's used in this way have a design life of 5 to 8 years.

However if you need a battery bank that will be in constant daily discharge cycle use all year round, then your battery bank should be sized so that your daily depth of discharge is about 20 to 25%, this applies to all types of deep cycle batteries if you want them to last for many years.
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