Best AGM Battery Charger UK

What is an AGM battery?

It’s a type of lead-acid battery, which is designed and built in a different way to “traditional” lead-acid batteries, with different technology. 

The acronym AGM stands for Absorbed Glass Mat. 

AGM batteries are still lead-acid batteries. It’s just that traditional lead-acid batteries have the electrolyte liquid (which is a mixture of acid and water) freely flowing around the battery plates.

AGM batteries, on the other hand, don’t have the electrolyte flowing around the battery – instead they have highly absorbent fibreglass mats with the electrolyte (acid and water mixture) soaked on them.

Advantages of AGM Batteries

• They charge more quickly than other lead-acid batteries
• Longer lifespan
• Completely maintenance-free, no need to top up with water
• Safer – they’re non-spill, even if the battery casing was cracked
• Low self-discharge rate – they can be stored for much longer than normal lead-acid batteries
• Don’t suffer from acid stratification (which causes major harm to other lead-acid batteries)

Charging AGM Batteries

AGM charging is unlike charging any other kind of lead-acid battery.

Read on and you’ll see that “normal” batteries chargers are not your friend; we’ll advise you what battery charger makers will say on their products about their AGM charging capabilities and how to interpret this; best charging voltages; why AGM batteries need to be charged differently; why AGM batteries must be desulfated (have their sulfation removed); and finally, the best AGM battery charger to get.

Can I Charge AGM Batteries With A Normal Charger?

The best advice we can give you is: no. Don’t do that.

Assuming by “normal” charger you mean a battery charger you already have which you’ve used before on normal lead-acid batteries.

If your charger doesn’t say specifically it’s made for AGM batteries, or doesn’t have an AGM Mode, then you shouldn’t use it on AGM batteries.

Some chargers say they “may” be suitable for AGM chargers. I think you can guess our opinion on this, but if not… steer clear.

If it says “Deep Cycle/Gel/AGM”

Some older chargers (and some poorer brands) may say something like the above – “Deep cycle/Gel/AGM”.

This lumps AGM batteries in with Gel and Deep cycle batteries but actually AGM batteries are charged in a completely different way to Gel batteries.

Chargers that are perfectly fine for Gel batteries my significantly undercharge AGM batteries, and even harm them over time. These are really not battery chargers for AGM.

If it says “Works with all lead-acid batteries”

Be careful with this phrase and similar ones.

Many chargers simply state: “works with most battery types” or “works with all lead-acid battery” or “suitable for most lead-acid batteries”. 

If they don’t even mention AGM batteries specifically, it’s a near certainty that they’re not suitable for AGM! As we said earlier, even if they don’t actively cause harm to your AGM battery they’ll never fully charge it, and then you’re on a downward slope to early battery death.

The Car Battery Geek team has heard stories of AGM batteries being turned into a hot, sticky mess by normal chargers!

And even if the battery charger does say it’s for AGM, take care…

Not All “AGM” Chargers Are Worthy of The Name

Some battery chargers that have an AGM mode or have AGM listed as a suitable battery type (but in reality, they just whacked AGM on their list of suitable batteries) have the following issue – they’ll charge your battery but only to around 85%.

This causes a harmful “memory effect” – the battery ‘remembers’ that 85% and that becomes the new maximum charge your battery can achieve. This causes a downward spiral, and the battery will end up dying much quicker than it would otherwise have lasted.

Why does this happen?

Well, it’s all about charging voltage.

AGM Battery Charging Voltage

The AGM charge voltage is 14.6-14.8V to properly charge from a discharged state; they need this voltage. This is compared to normal lead-acid batteries, which need 13.8-14.4V.

Since most normal lead-acid batteries charge at this lower voltage, this is what most battery chargers are designed to deliver, rather than the higher voltage required by AGM batteries.

If AGM batteries don’t get this higher voltage, they won’t get charged properly – and that means they’ll get sick faster.

Full Charge Voltage

Full charge voltage (the voltage the battery itself will reach, not the charging voltage provided by the charger mentioned above) is 13.0 volts, or above. Generally, only a fully-optimised AGM-specific charger will be capable of getting your battery to this full charge status.

AGM Charging – How to Maintain

Here are the best practices for AGM battery maintenance to make sure your AGM battery lasts as long as possible.

1.) Fully charge it every time

Especially if it’s going to be stored rather than used.

As mentioned earlier, that’ll be to 13.0V or more.

2.) Don’t trickle charge your AGM battery.

That means: don’t leave it on permanent charge. This can be a good idea for other battery types, but not AGM. Even with no electrolyte (battery acid and water mixture) flowing around inside, it will make the battery dry out.

Should I Use A Trickle Charger For AGM Batteries?

Don’t use a trickle charger/maintainer (a charger that provides only a trickle charge), since the voltage won’t be high enough to properly charge the AGM battery.

What to do instead?

When it’s fully charged, either store it or use it as normal (depending on how you use this battery) and give it a charge once a month, that will be fine. You can easily charge it overnight.

The final step of CTEK and NOCO’s (more on them later) battery chargers’ AGM mode is a trickle charge (termed Float Mode and Pulse Mode by CTEK) – since that’s the type of charge needed at that point to stay fully charged.

This is fine – since the battery is fully charged.

But AGM have slow rates of discharge, you just don’t need to keep it permanently charging the way you sometimes would would with normal lead-acid batteries. 

3.) Keep your maximum discharge down to 50%. On AGM batteries, this is 12.1 volts.

If you allow them to discharge lower than that, you will lower the lifespan of the battery.

Why Do AGM Batteries Need To Be Charged Differently?

Charging AGM batteries is different, no doubt. The question is, why? 

Well, it’s all to do with the construction of AGM batteries, which differ significantly to traditional lead-acid batteries.

Most traditional lead-acid batteries are Flooded (Wet).

Flooded batteries have a liquid electrolyte (mixture of battery acid and water) which is free to flow around the battery.

But AGM batteries use a stabilised electrolyte (the electrolyte is immobilised, not free-flowing). The electrolyte is absorbed in a glass mat (which is where Abosrbed Glass Mat, or AGM, comes from). Therefore, the electrolyte cannot be spilled, even if the case was punctured. 

It’s for this reason that AGM batteries can also occasionally be called dry batteries.

Flooded batteries are still widely used today as they are lower cost and can deliver a large burst of energy to start engines. The downside is they need more ventilation, maintenance and are quicker to discharge.

AGM batteries lose charge much more slowly and are more stable.

Different Construction = Different Charging Needs

It’s easy to imagine, then, that since AGM batteries have a very different construction – with their electrolyte absorbed onto fibreglass mats –  the way it accepts charge is also very different.

A battery charger that is built for normal Flooded car batteries only can harm AGM batteries, and may even cause them to burn out and die.

Which Charger Should I Get?

This is what you need:

1.) Reputable brand which can be trusted to have an AGM-specific mode.

People with other battery types may get away with using less reputable brands, but you need to be sure your battery charger is genuinely okay for AGM batteries.

2.) A charger with built-in desulfator function

This is a function of the charger that removes sulfation from the battery plates.

Conditioning AGM Batteries

Just as with all lead-acid batteries, AGM batteries suffer from sulfation as well.

What is sulfation?

It’s the build up of lead-sulfate on the plates of the battery. Sulfation is what causes more than 80% of batteries to die.

It’s a natural process, an unavoidable part of the chemistry of lead-acid batteries… but, it’s reversible. Modern desulfating chargers can effectively remove the sulfation from the battery plates, while they charge.

Desulfating AGM batteries by using a desulfating charger (how do desulfating chargers work?) can make your batteries last 2 or even 3 times longer than they would last otherwise.

If you want to really maximise AGM battery life, you can also use a desulfator. This is a small unit that permanently attaches to your battery and gives a high-frequency pulse to the battery, breaking down the lead sulfate. It’s always removing sulfation and never letting it build up in the first place.

Battery desulfation, then, can significantly extend battery life and improve power delivery. To really maximise your battery’s lifespan, consider F16 Pulse King, a desulfator. It removes existing sulfation and prevents any sulfate crystals building up in the first place.

As for battery lifespan, here’s how long car batteries last in the UK.

The Best AGM Battery Chargers in the UK

There are two brands that you can be utterly confident about using for AGM batteries – CTEK and NOCO.

These two are by far the biggest battery charger makers and most importantly they have AGM Modes. Unlike some makers, these modes have genuinely been built for AGM batteries, so you need not have any safety concerns.

Apart from being the safest and best charging option for AGM-specific, they have the most sophisticated charging process – in our estimation, the CTEK in particular.

And they have the best desulfation modes. These have the genuine ability to significantly lengthen battery life. AGM batteries are not the cheapest – so these CTEK and NOCO battery chargers could end up saving you money, if your battery does last 2 or 3 times longer, as is possible.

To help your decision, here’s the NOCO 10 reviewed (NOCO Genius 10 UK), and here’s the CTEK 10 reviewed (CTEK MXS 10). Or go straight to Amazon, by clinking on the pictures below, if you want to check it out.