Charging cables and adapters are a common source of consternation. Can a lead-acid charger be used to charge a lead-acid battery? A short "it depends" sums up the situation nicely.

There is a wide variety of battery types available. There are rechargeable batteries and there aren't. Rechargeable batteries, too, come in a variety of shapes and sizes. Common battery kinds include lead-acid, nickel-cadmium, and lithium.

Compared to its sealed lead acid equivalents, lithium batteries can be charged far more quickly. You've probably heard that lithium batteries charge rapidly, but how much faster are they than standard lead-acid (SLA) batteries? To what extent does this affect you as a consumer? Finally, can a regular sealed lead acid charger be used to charge a lithium battery?

How battery chargers work

When fully charged, lithium batteries have a shorter operating window of voltage than their lead-acid counterparts of same specification.

In order to charge, lithium batteries require a constant current source, which is provided by the charger until the battery is full. A lithium battery charger does not have a 'float' or 'trickle charge.

The 'rapid charging' capability of lithium battery chargers is reliable. When charging a battery, they can send a large amount of current until the battery is nearly full, at which point they slow down the charging process.

The charging process for lead-acid batteries is threefold. These steps are:

l lBulk

l lAbsorption

l lFloat

Fast charging occurs during the bulk phase, which fills the battery to around 80% capacity. The battery's internal resistance prevents it from accepting the full rate of charge at that state of charge, hence charging proceeds more slowly during the absorption stage.

When the battery's current consumption drops to a trickle or the battery charger remains in the absorption stage for about four hours, the float stage begins.

Many factors can contribute to this, including charging too many batteries at once or using a charger that isn't strong enough for the battery.

Some "smart" chargers analyze the battery's condition before beginning charging, deciding at what stage to begin. As a result, the battery is protected while receiving the maximum possible charge.

Charging absorption is different for SLA and Lithium.

You know how time consuming it is to wait for a SLA battery to charge before you can use it in a gadget if you've ever had to do that. For reference, it took around 6.5 hours to fully charge a 12-volt, 20-amp-hour deep cycle SLA battery. However, the lithium iron phosphate battery with a capacity of 20 amp hours required slightly more than 2.5 hours to attain 100% SOC.

SLAs have a three-step charging cycle consisting of a constant current phase, a constant voltage phase, and a float charging phase. The battery is fully charged during the constant current phase. During this phase, the 20Ah deep cycle SLA battery has reached 80% State of Charge (SOC), or slightly over half way through the charging process. About half of the total charge time is spent in the constant voltage charge, also known as the absorption charge, which charges the remaining 20% of the battery. Additionally, for most applications, keeping the battery on a float charge is recommended to avoid over-discharging the battery due to the chemistry's inherent self-discharging properties.

However, there are just two stages of constant current and constant voltage in a lithium charging cycle. It takes only 96% of the total charge time for the battery to absorb 99% of its capacity (SOC of 99%) at the constant current/bulk charging stage. In the case of the 12.8V 20AH lithium battery used in the previous example, this means that full charge is achieved in under two hours. With only a 4% increase in charge time, the constant voltage charge stage adds only 1% to the capacity. Because of its low self-discharge, lithium batteries also don't need to be kept on float charges.

In this case, the lithium battery fully charges in one-third the time it takes to charge a SLA battery to the constant voltage stage of its charging cycle. This is crucial in applications with frequent on/off cycles, as devices must be removed from service while being charged. Because of the time it takes to fully charge bigger SLA batteries, it may be necessary to have a backup supply of batteries at all times.

Lithium absorption on a SLA charge profile

Those familiar with lithium and sealed lead acid battery charging profiles may wonder what would happen if a lithium battery was used in place of a SLA battery in an existing device. Would doing this kill the battery? How well does the lithium battery handle fluctuating voltages and float charging?

Lithium batteries can be charged to 95% capacity in roughly 90% of the entire charging time when using a SLA charger at 13.8v bulk charge (the normal float voltage for SLA and a common voltage for basic chargers). It just takes 10% of the float charging time to use up the remaining 5% of capacity. This lithium battery would have been charged to 99% capacity in 95% of the total charge time using a 14.6V bulk charge (typical constant voltage for charging an AGM battery; selected because lithium is typically a drop-in replacement for AGM batteries).

When charging lithium on a SLA profile, the charge time will be longer; for example, a 20AH lithium battery charged using the lithium profile above will take around 2.5 hours to fully charge, but the same battery charged using the SLA profile will take about 5 hours. Charging a lithium battery still takes less time than charging an equal SLA battery using a SLA profile, as can be seen in the table below.

Those familiar with lithium and sealed lead acid battery charging profiles may wonder what would happen if a lithium battery was used in place of a SLA battery in an existing device. Would doing this kill the battery? How well does the lithium battery handle fluctuating voltages and float charging?

Lithium batteries can be charged to 95% capacity in roughly 90% of the entire charging time when using a SLA charger at 13.8v bulk charge (the normal float voltage for SLA and a common voltage for basic chargers). It just takes 10% of the float charging time to use up the remaining 5% of capacity. This lithium battery would have been charged to 99% capacity in 95% of the total charge time using a 14.6V bulk charge (typical constant voltage for charging an AGM battery; selected because lithium is typically a drop-in replacement for AGM batteries).

When charging lithium on a SLA profile, the charge time will be longer; for example, a 20AH lithium battery charged using the lithium profile above will take around 2.5 hours to fully charge, but the same battery charged using the SLA profile will take about 5 hours. Charging a lithium battery still takes less time than charging an equal SLA battery using a SLA profile, as can be seen in the table below.

Can a normal SLA charger damage a lithium battery?

Is it OK to use a SLA battery charger on a lithium battery, or would it cause damage? If the charger does not feature a de-sulfate mode, the battery will likely not degrade in highly cyclic situations where it is cycled everyday and may never see the float charge. Also, the SLA charger might not be able to bring the lithium battery up to full capacity (for instance, a 20AH lithium battery might only go up to 18 amps). Disconnecting the battery from the charger before storing it is recommended if you won't be using the battery frequently and it will spend a lot of time on a float. An aside: lithium is at its optimal state of charge (SOC) when kept at 50%. To sum up, a lithium battery can be charged with a standard SLA charger (without the de-sulfate mode).

Kowint Energy recommend that batteries be charged using a charger designed for their specific chemistry. Every three to four months, you should check your lithium batteries for low voltage and recharge them if necessary.

Charging a LiFePO4 battery: lithium charger vs. lead acid charger

See how a 12V lithium battery charger compares to a lead-acid one for recharging your LiFePO4 batteries.

Voltage Restriction

In order to prevent damage to LiFePO4 batteries from being overcharged, most chargers have a voltage-limiting feature. These include more stringent controls in order to reduce the dangers associated with overcharging, such as fires. In contrast, the voltage cut off on standard lead acid chargers can be adjusted more precisely.

You must double check that the pricey electronics necessary to correct for these charging variances are present in your lithium battery before utilizing a lead-acid type charger on your modern caravan or automobile.

Charging Profile

Charging lithium-ion batteries to 100% SOC requires a slightly greater charge voltage and a deeper steady voltage at the conclusion of the cycle. Even while lead-acid charging profiles can get pretty close (maybe 95% efficient), they cannot get there.

The two batteries also exhibit differing "return to boost" behavior during the charging process. The lithium battery charger checks the battery voltage immediately following a full charge cycle to determine if it should return to boost/bulk charge mode and begin another full charge cycle.

In contrast, lead acid batteries typically wait until the voltage is quite low before beginning the charging process again. One reason is its lower resting voltage in comparison to lithium batteries.

What's the best way to charge a lithium battery?

Therefore, how do you charge lithium batteries? The first step is to use a suitable lithium battery charger and to keep the voltage within safe parameters.

Temperatures above 32 degrees Fahrenheit (0 degrees Celsius) are acceptable for charging lithium-ion batteries. If you must charge it when the weather is below freezing, do it at a current of 5-10% of the battery's capacity.

Lithium-ion battery parallel charging

Before interconnecting your batteries in parallel, make sure the voltage of each battery is within 50mV by charging it separately and verifying it. This will aid in maintaining optimal battery performance by reducing the potential for voltage differences between cells.

Series charging of lithium-ion batteries

Power packs can be connected in series to achieve the same effect. Using a multi-bank charger, in which each battery is charged independently to preserve cell balance, is recommended for optimal performance.

Always employ a solar charge controller (ideally an MPPT charge controller) between your battery bank and solar panels while charging your battery with solar electricity. This controls the flow of power from your panels into your power pack.

Precautions to take when charging a lithium battery

1. Regular charging and discharging of a lithium battery is essential for extending its service life. Electric vehicles should be charged after utilizing 80 percent of the electricity, rather than waiting until the battery is completely depleted. It's also not a good idea to keep lithium batteries around for too long.

2. The electronic door lock must be in the locked position and the battery must be in the correct orientation for charging if you have an electric vehicle. It's best to charge it all the way up in one go rather than topping it off numerous times.

3. Never let the power go out on an electric device before putting it away. That's why, once a month while the battery isn't in use, it needs a full charge.

4. The correct charger must be used to charge a lithium battery. Battery raw materials and lithium battery production processes are two factors that influence the charger's technical specifications. As a result, only a special charger can extend the life of the lithium battery. avoid potential dangers, etc.

5. When the lithium battery is depleted, the power supply must be turned off before riding, and the recovery voltage must be avoided to avoid catastrophic discharge.

6. When charging the electric vehicle's lithium battery, it's not a good idea to immediately cease charging when the charging indicator shows that the battery is full.