In the olden days, you had this thing called a car battery. Lead, acid, you’re done.

Nowadays, there are so many different types of lead-acid batteries. Plus, everyone will give you different advice on which battery to choose.

Is it for a car with Start and Stop? Can you use a new-fangled battery in an old-fangled vehicle?

Which one lasts longest? Gives you the most energy? The best bang for you buck?

Read on for a simple guide to lead acid batteries!

Let’s get the acronyms out of the way

I’m an engineer, so I love acronyms. You probably don’t. So here’s what it all means:

• FLA – Flooded Lead-Acid battery. Old school. Usually you must top up the water levels.
• SLA – Sealed Lead-Acid battery. It’s sealed, so no spilling, no filling!
• VRLA – See SLA
• EFB – Enhanced Flooded Battery. Fancier than SLA, not as fancy as AGM. Works for Start & Stop
• AGM – Absorbent Glass Mat battery. Fanciest, most expensive, for Start & Stop

Okay, so all done, right?

Wrong! It’s complicated

So, the short version is this:

Whatever type of battery your vehicle has, replace it with the same type of battery! DONE.

The Longer Version

Oh boy. Well, you asked for it…

FLA

In the olden days, we had FLAs. Lead plates, sulfuric acid + water. Every now and then, you probably would need to unscrew the battery caps, add pure water, and then carry on.

There was usually also a little vent pipe, because the chemical reaction in the battery produced gas, and an exploding battery is a bad thing.

SLA

Then came the SLA, which is like the FLA, but sealed! Yay! No more adding water, no more venting, and all was right with the world. Sometimes these are called VRLA because manufacturers think it makes their battery sound cooler than everyone else’s batteries.

Ah, progress…

But then, technology advanced. Our cars became fancier, and many started including the semi-ridiculous Start & Stop system.

By turning your engine off when you’re stopped at a traffic light, Start & Stop systems were supposed to save the earth. That’s ridiculous, but whatever…

Your normal lead-acid battery probably has enough juice to start your engine maybe 10 times. It’s also best to recharge the normal SLA batteries slowly, like 0.1C. That means that for a 12V, 60Ah battery, ideally you’d charge it at a max of 0.1 x 60A = 6A.

This creates a problem because if during your 10-minute drive to the grocery store,  your Start & Stop engine cuts out 5 times, you actually need 6 starts instead of just 1 for that 10-minute trip.

Plus, your car has all sorts of electronic goodies, like ass-cooling seats and a touchscreen internet connection and Spotify and god knows what else.

So, it’d be better to have a battery that could be recharged faster and that could supply more juice.

BEHOLD, the EFB!

Enhanced flooded batteries have a sort of “matting” around the lead plates, plus some other stuff I won’t get into. Long story short, they’re more resistant to heat, give you more starts, and you can recharge them almost twice as many times as a standard battery – with a bit more charging current. Yay!

But still, you can do better… That’s where AGM batteries come in.

AGM

AGM batteries have a fiberglass-type matting that absorbs all the liquid in the battery. They’re superduper, and can be recharged at 2.5X to 5X the rate of a normal SLA battery! Super-good for Start & Stop! They’re not quite as heat-resistant as EFB batteries, but when it comes to heavy use, they rock.

You can also safely discharge most AGM batteries to as low as 20%, whereas it’s only 50% for SLA/EFB.

Why can’t I swap in a fancy AGM battery for my SLA or EFB?

Now that’s an interesting question. It IS possible to use an AGM battery in place of an SLA, or even vice versa. I just don’t recommend that you do it.

The reason is that ideally, AGM batteries charge very differently from EFB and SLA batteries. So if your vehicle came with an AGM battery and you stick an EFB in, your EFB battery might not last very long.

Similarly, if you have an SLA/EFB and you just plop in an AGM battery, you MIGHT luck out and it’ll be okay – but most likely, you’re looking at a much shorter battery life for your expensive AGM.

It comes down to how AGMs and SLA/EFBs are charged. For example, you often hear that the typical charging voltage for an AGM battery is 14.7 V. For SLA/EFB batteries, it’s 14.4 V. That may seem like a tiny difference, but that’s not all you need to worry about.

The charging voltage actually changes over time, and so does the current level… Get those wrong, and you shorten the life of your battery dramatically.

AGMs have a lower internal resistance, and that helps allow faster recharging rates. But you can’t just do whatever you want. Most vehicles with AGM batteries have more strict battery charging control. Stick a normal SLA in there, and you’re gonna bork it.

So, if your vehicle came with an SLA, replace it with an SLA (or EFB – that’s okay in this case).

If your ride came with an EFB, then EFB it is!

And if it came with AGM, then get a new AGM.

One final note

A lot of battery manufacturers are including all kinds of weird claims and acronyms on their batteries. If it’s not clear to you what you’re buying, then don’t buy it.

Many of these companies are trying to sell EFB batteries as “one size fits all” solutions, and that’s just not right.

There are differences between battery types, and no one technology covers all the bases. I have used the wrong battery type in vehicles, and it was a very expensive mistake. AGM is NOT always better…