How To Replace Lead Acid/AGM Batteries With Lithium-ion Batteries

Replacing lead acid/AGM batteries with lithium-ion can be either a simple, straightforward process or a complicated one, depending on the application. Due to their many advantages across a wide range of applications, it’s becoming more and more common to replace lead acid/AGM batteries with lithium.

If you are upgrading a home battery bank to lithium and you already have a modern charge controller, the process could be as simple as installing the new batteries and flipping a switch. If, however, you are replacing a lead acid/AGM battery with lithium in a vehicle or RV, then you must consider the capabilities of the alternator. Lithium-ion batteries will take pretty much as much current as you can give them. The current coming from an alternator is entirely unregulated, so replacing a lead acid/AGM battery with a lithium battery can overheat or even destroy your alternator and its wiring. In these cases, it’s good to use a DC-to-DC buck or boost converter between the alternator and the battery to ensure that only a set and limited amount of current is drawn from the alternator.

When upgrading a 12-volt lead-acid powerwall or off-grid battery with lithium-ion, a 4S LFP configuration is always going to be the best solution. When upgrading a 24-volt or higher off-grid battery to lithium, however, a wide selection of chemistries and configurations are viable. Scooters are particularly easy to upgrade from lead acid to lithium-ion because they generally only contain a single, 12-volt battery. Golf carts, on the other hand, usually contain an array of batteries with a voltage of either 12, 24, or 48 volts. In either case, motorized equipment generally accepts a much wider-than-stated voltage range, which makes several lithium-ion battery chemistries viable for these applications.

In this article, we will explain how to replace a lead acid or AGM battery with lithium. We will cover several popular lead acid conversions as examples, and we will also go over the key differences between lead acid / AGM and lithium in terms of performance, size, reliability, and cost.

Can You Replace The Lead Acid Battery With Lithium?

Yes. Any lead acid or AGM battery can be replaced with a lithium battery. A more specific question would be, ‘What is the best type of lithium better to use to replace lead acid/AGM for a given application?’

There are several different lithium battery chemistries and many different configurations that the cells and battery packs can be put in. So, knowing more about how lithium-ion batteries work and the differences between various cell chemistries is crucial to the process. The two main chemistries for conversion are LifePO4 (LFP) and Lithium Nickel Manganese Cobalt (Li-NMC).

Lithium-ion batteries have a BMS (Battery Management System) built into them. This means that the battery will automatically prevent itself from becoming over-discharged or overcharged. Also, lithium-ion batteries can be mounted in any position as there is no acid or other liquids inside that could leak out if they are turned upside down.

Another thing to consider is that lithium-ion batteries last anywhere from 5 to 10 years. That’s around twice the life expectancy that lead acid batteries can provide.

How To Replace A Lead Acid Battery With Lithium

Converting 12v Powerwall / Off Grid to Lithium

The first step in upgrading a 12-volt lead acid battery to lithium is to choose the cell chemistry and configuration. This is a necessary step because regardless of the chemistry you use, lithium-ion batteries have a voltage that is much lower than 12. This makes it so you will have to put some amount of them in series to achieve 12 volts.

This task is simple enough up to this point, but then one must consider that all batteries operate along a voltage curve. Whatever configuration you put whatever number of whatever type of cells in, its fully charged voltage will be higher than its normal running (nominal) voltage and much higher than the dead voltage.

This situation can make it so that whatever you are powering works just fine when a 4S NMC lithium battery is not fully charged, but once the battery is fully charged, the voltage can end up being too high, resulting in damage.

In other cases, whatever you are powering will work just fine when the 3S NMC lithium battery is fully charged and will stop working when the battery appears to die. All is normal, right? Well, what’s really happening is that the voltage is falling below a certain threshold (usually 10.5 volts for 12V equipment) and the device can no longer run even though there is still plenty of energy left in the battery.

So, if you are wanting to make a 12-volt lithium battery, then the best chemistry to use is going to be LiFePO4. LiFePO4, or LFP, cells have a discharge curve that almost exactly matches the discharge curve of a 12-volt lead acid battery.

This is because LFP cells have a nominal voltage of 3.25V. So, putting four LiFePO4 cells in series provides a fully charged voltage of 14.4 volts, a nominal voltage of 13 volts, and a dead voltage of 10ish volts.

In contrast, with NMC lithium-ion cells the closest you can get to 12 volts is 3 cells in series. This leaves you with a fully charged voltage of 12.6 volts, a nominal voltage of 11.1 volts, and a dead voltage of somewhere just south of 8 volts.

Converting 24v Powerwall / Off Grid to Lithium

It’s a different story for 24v, 48v, and higher voltage off-grid lead acid systems. Remember, the problem with 12 volts was not really the batteries, the BMS, or the chemistry. The problem lies in the equipment operating range. Most ‘12 volt’ equipment is designed around a 4-cell lead acid (12 volts) battery. This means that most 12-volt equipment will be just fine with 14 or so volts and will happily run until the battery hits about 10 and a half volts or so.

So, taking this knowledge forward and into high voltages, the same thing applies. It’s all about the voltage range. If something is made to work with a 24-volt or 48-volt range, then it generally has a wide enough operating range that several different types of lithium-ion chemistries can be a variable lead acid replacement.

This means that if you are powering a 24-volt inverter or most other things that are rated for 24 volts, it will really be able to run on anything between around 18 and 30 volts. These are of course general numbers and you should always refer to your specific equipment for its operating voltage range.

Replacing Lead Acid Scooter Battery With Lithium

Replacing lead acid in a scooter is easy. This is because scooters are generally powered by just a single 12-volt lead acid battery with a capacity of about 8 amp hours or so. Lithium batteries are a lot more power dense than lead acid or AGM batteries, so this means that a replacement lithium-ion battery of the same capacity will be much smaller than a lead acid battery.

So, buying or building a lithium-ion battery for a lead acid scooter is a relatively straightforward affair. Another thing that makes it even easier is the fact that devices that use motors such as drills, ebikes, and golf carts, can generally run on a much wider operating range than the original lead acid battery.

This makes it so you can replace a 12V lead acid scooter battery with either a 3S NMC lithium-ion battery or a 4S LFP lithium-ion battery. In fact, you can more than likely go even higher than that, but again, these are general statements and you need to look into the capabilities of your device.

When upgrading a lead acid-powered device to a lithium ion-powered device, it may be hard to find the true maximum operating voltage as the manufacturer will usually simply state the running voltage range of its originally supplied battery. This is when it’s good to check out Facebook, Reddit, and other online platforms to see what other people are upgrading their voltages to.

If you don’t plan on increasing your voltage much or at all, then you generally don’t even have to worry about changing the controller in your electric scooter. You really only need to upgrade the controller when converting a lead acid scooter to lithium-ion when you want to upgrade the motor or substantially overvolt the stock motor.

How to Upgrade Lead Acid Golf Cart To Lithium

When replacing a golf car lead acid or AGM battery with a lithium-ion battery, there are many options. Golf carts are not high-speed, high-power vehicles. This means that the battery requirements for them are often much lower than with scooters and ebikes.

This gives a lot of flexibility in terms of what type, size, and voltage lithium-ion battery that you put in your golf cart. In circumstances like this, our battery pack planner will be very helpful to help you optimize your build. Like other motor-based equipment, if a golf cart is rated to run at 24 volts, it will really run on a much wider range. You may be able to take this opportunity to not only upgrade your gold carts reliability and range but to also substantially upgrade its performance while you’re at it.

Cheaper or older golf carts are generally 24-volt vehicles. This, combined with the fact that motors can often support higher-than-rated voltages, means that you can easily upgrade any 24-volt golf cart with a 7S NMC lithium-ion battery. This setup would give your golf cart a new nominal running voltage of 25.9 volts and a dead voltage of just under 20 volts.

This means that throughout the entire running voltage of your lithium-ion battery, your 24-volt golf cart will be faster than it was with the original battery at the same level of discharge.

Considerations When Converting Lead Acid/AGM To Lithium

Charging Lithium Converted Devices

Lead acid batteries require a simple constant voltage charge to the battery while lithium ion chargers use 2 phases; constant current and then constant voltage. Unlike lead acid batteries, Lithium-ion batteries have an extremely small capacity loss when sitting unused.

Depending on how recently you purchased or built your lead acid setup, you may already have a charge controller that can work with lithium-ion batteries. Maybe off-grid lead acid installations use more-or-less universal charge controllers that support many different types of battery chemistries.

So, take a look at your charge controller and see if there are any settings to change the chemistry type. Also, there may be LED or LCD indicators that show ‘Lead Acid’ or ‘AMG’ as the currently selected type. If you see this, then chances are there is an option to switch it to lithium-ion.

If your charge controller makes no mention of lithium-ion, you may be able to get away with still using it if you plan on using LiFePO4 batteries as they are much more forgiving and much safer than their lithium-cobalt counterparts. This, however, is not recommended as all lithium batteries work best with a constant current charger. Most lead acid systems are constant voltage and not constant current.

Another option for charging your pack is to build a lithium charger this will give you greater flexibility. The downside is the process of building a charger yourself can be tedious.

Mounting Lithium Battery

Watt-hour for watt-hour and amp for amp, lithium-ion batteries are much smaller and much lighter than their lead acid and AGM counterparts. This means that if you are upgrading something from lead acid to lithium-ion, you need to take a look at how the battery is mounted.

Chances are, the battery is mounted in such a way that depends on its size and overall bulk. For example, a mounting strip may fit perfectly on the large, stock lead acid battery, while not even making contact with the smaller, more powerful lithium-ion battery.

This issue can be avoided by simply taking advantage of the additional space. Remember, if a lithium-ion battery that is smaller than a lead-acid battery can have the same capacity, then a lithium battery that is the same size as a lead-acid battery can have a much higher capacity. It’s important to keep in mind on average lithium weighs 55% less than lead acid at the same capacity.

Temperature Variance of Lithium Compared to Lead Acid

There is a common misconception that lead acid batteries produce less heat and can handle more amps than a lithium-ion battery. This is false. The reason people think this is because lead acid batteries must be much, much larger than lithium-ion batteries in order to be competitive with them at all.

Because of this already-required extra size due to the low power density of lead acid and AGM battery chemistries, there is already plenty of room for massive, fat electrodes to pump the current out of the cells. Those large electrodes can handle a lot of heat internally before that heat is expressed on the outside.

While it’s true that for a given amount of current, a lithium-ion battery will produce less heat, a lithium-ion battery of equal size to a lead acid battery, however, is able to produce much more current in a given space. If this higher level of current is accessed, at some point the battery and everything in the battery compartment will get much hotter than it was ever designed to deal with.

Because of this, when using lithium-ion batteries to get more power out of something rather than just getting more range, care should be taken to monitor the temperature of the battery during operation. The good news is that any smart BMS will do this for you and provide the info in the app, and many non-smart BMS will also do this for you and simply shut down the battery when the temperature gets too high.

If you’re not sure, we recommend you check with your BMS manufacturer to see if temperature monitoring is something that your BMS supports.

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Replacing Lead Acid/AGM With Lithium In Cars, Boats, and RVs

Things get a little complicated when alternators are involved. While it’s true that alternators are voltage regulated, they are not current regulated. This means that the alternator will provide as much current as you ask from it, even if you are asking too much.

One of the great benefits of lithium-ion batteries over lead acid/AGM batteries is their ability to charge much faster. In the area of vehicle battery upgrades, this can be a downside. If you use a significant amount of battery power while your engine is not running, the voltage of your lithium-ion battery will slowly drop.

This is normal for all batteries. The difference, however, is that when a lithium-ion battery has a voltage lower than its power supply, it will consume as much current as it possibly can to make up that difference in voltage.

This can cause your alternator and its power cables to overheat and could potentially start a fire that you cannot put out. Also, even if the alternator could handle the intense amount of current, this is not the proper way to charge lithium-ion batteries. To avoid overheating it’s important to size wire correctly.

Lithium-ion batteries require a constant current charge phase for the main part of charging the battery. Only at the very end does the lithium-ion charge process switch to constant voltage mode. For this reason, it’s essential to put some sort of current limiting device between the alternator and a lithium-ion battery.

Benefits of Replacing Lead Acid/AGM Batteries With Lithium

So let’s say that you need 25Ah to make it through the night. With a lead acid setup, you would need at least 50Ah of available capacity because lead acid batteries have only a 50% depth of discharge. With a lithium setup, you would only need about 30Ah of available capacity to make it through the night without any loss of power.

When it comes to AGMs and lead acid batteries vs lithium, lithium batteries will always be lighter, more powerful, and more efficient. Due to the problem with the depth of discharge, you will physically need more AGMs or lead acid batteries, which drastically increases weight.

On top of that, lithium batteries store much more energy pound-for-pound compared to the old type of batteries. This makes it so that lead acid and AMG systems get really heavy, really fast.

It’s pretty common for modern RVs to have 400Ah or more of AGB battery capacity. This rating, however, is not exactly accurate. AGM batteries cannot be discharged any more than 50% without permanently damaging them. So that means the usable capacity is closer to 200Ah.

That means you can replace 4 AGM batteries with two smaller 100Ah lithium batteries without losing any available capacity.

Conclusion

As you can see from the length of this article, when it comes to replacing lead acid/AGM batteries with lithium-ion, there is quite a bit to learn and take into consideration. If you keep a few key concepts in mind, however, you will be on the right path to upgrading your equipment properly.

When upgrading a 12-volt home battery bank or powerwall battery, it’s best to LiFePO4 (LFP) cells because their cell chemistry is ideal to match the requirements of devices made to run on a 12-volt lead acid battery. When replacing a 24-volt or higher off-grid or powerwall battery with lithium, however, several configurations and chemistries are viable to use. Any time you are replacing a lead acid battery with a lithium-ion battery in a vehicle, you have to take the alternator into consideration. This is because lithium-ion batteries can charge much faster than lead-acid batteries can, so without a regulator, most alternators will become overloaded. This makes a DC-to-DC converter necessary when properly retrofitting a lithium-ion battery into a car, truck, or other vehicles that use an alternator to charge its battery.

If you plan on upgrading a lead acid scooter with a lithium-ion battery, you are in luck as that is probably the easiest lead acid to lithium-ion upgrade you can do in a vehicle. Golf carts, while larger and more complicated, are equally as straightforward to upgrade to lithium-ion batteries. This is because motorized equipment often has a wide operating range.

Source:

https://cellsaviors.com/blog/lead-acid-agm-lithium-replacement