Why Is Charging A Lithium Battery Different?
Lithium batteries charge in a very similar way to lead-acid batteries (including AGM & Gel batteries) but there are a few important differences.
Related Product: Track any 12 volt battery’s charge with the Quicklynks Bluetooth Battery Monitor (click to view on Amazon)
The optimal charging of a lithium ion battery has two phase; CC (constant current) and CV (constant voltage).
During the CC phase, the voltage starts low and gradually increases while the current (amperage) starts high and stays at the same level.
Once the lithium battery reaches the max voltage (usually around 14.4) the second phase will begin. During this phase the current will decrease and the voltage will stay the same.
A good battery charger for lead-acid batteries will have 3 phases; bulk, absorption, float. Sometimes you will see 4 stage chargers that include an equalization mode but this isn’t a must have for proper battery charging.
The bulk phase is very similar to a lithium charger CC phase. It starts with a high constant current and increasing voltage.
The second absorption stage is the most similar to the CV phase for lithium batteries. The voltage stays constant and the current drops.
The 3rd float stage is the one that’s unnecessary for lithium batteries and the phase that could damage them.
During the float stage, a charger maintains a lead acid battery’s charge by keeping a constant voltage and increasing the current when necessary.
Lithium batteries don’t need this step because being held at the high 14.4 voltage isn’t good for them, it actually decreases their lifespan.
It’s better to stop charging once it reaches a full charge and to let the lithium battery rest afterwards.
NOCO Genius 5 Charge Modes
The NOCO Genius 5 (click to view on Amazon) is a smart 5 amp battery charger that supports every type of 6 and 12 volt lead-acid batteries, and 12 volt lithium ion batteries that are smaller than 120 amp hours and have a BMS.
There’s even a mode for AGM batteries and a 4th phase repair mode for flooded lead-acid batteries.
I’m going to focus on the lithium battery mode in this post, but you can read more about the NOCO Genius 5 in this review.
Charging a Lithium-ion Battery with the NOCO Genius 5
If you read the manual that came with your 12 volt lithium battery, it probably recommends a 20 to 50 amp lithium battery charger.
The NOCO Genius 5 manual states that it can charge any 12 volt lithium battery with a BMS (battery management system) and an Ah rating of 120 or lower.
But the max current of the Genius 5 is just 5 amps, and both of my batteries have a 20-50 amp charger recommendation.
I did some research and from what I gather it’s ok to charge a lithium-ion battery with a low current.
See Also: When To Charge A Deep Cycle Battery
The reason companies recommend 20-50 amp chargers is simply because it will charge the battery faster.
A 20 amp lithium battery charger could charge a 100 amp LiFePO4 battery in about 5 hours. A 50 amp can do it in about 2.
The ability to charge quickly is one of the biggest pros to a lithium battery, especially for RVers who charge RV batteries with solar panels.
But just because you can use a high current battery charger it doesn’t mean you have to.
The NOCO Genius 5 charged both of my lithium batteries, but there are a few things to consider before you go out and get a one to charge your lithium batteries.
I’ve already mentioned this, but the charge time can be a big factor if you need to use the lithium battery in the next 24 hours.
The NOCO Genius 5 is going to take almost a day (20 hours) to charge if the battery is down to 20% or below.
If you can avoid it, try to never discharge a lithium-ion battery below 20%. Fully discharging lithium batteries damages them.
Battery Charger Overheating
The main thing I noticed when the NOCO Genius 5 was charging a lithium battery was how hot it was getting.
I only discharged the battery to about 70% and even in the second phase, the Genius 5 seemed to work really hard.
I think if I was using this battery charger for lithium batteries daily, it would eventually start having issues.
I’m not trying to knock on the quality of NOCO products here, but I think there are some limitations.
When charging my AGM RV battery, the Genius 5 doesn’t get nearly as warm and it works fantastically.
It’s an excellent choice for all kinds of 6 an 12 volt lead-acid batteries, and it’s a good option for occasionally charging a lithium battery.
But if I was going to be regularly charging my lithium batteries with a battery charger, I would go with a larger 20 amp charger like the ExpertPower 12V 20A Smart Lithium Battery Charger (click to view on Amazon) instead.
It’s made specifically for lithium batteries and it’s easy to use.
Luckily, I use a solar panel and compatible charge controller for the lithium batteries, so my NOCO Genius 5 won’t have to charge them very often.
If you want a charger that can do it all you can get the NOCO GeniusPro 25A Smart Charger (click to view on Amazon). But it’s more of a commitment and there are a lot more settings sort through.
Why did the voltage in my lithium battery drop after charging?
A 12 volt lithium battery will reach around 14.4 volts when fully charged but slowly level off to around 13.4 volts as the cells return to their true/resting voltage.
The reason lithium ion cells drop voltage like this has to do with the behavior of the lithium ions moving between the cathode and anode.
The extra voltage is eliminated and the battery that was charged to 14.4 volts will end up being around 13.4 – 13.6 volts about 30 minutes after you remove the charger.
The voltage may have dropped but the lithium battery is still 100% charged.
So don’t worry, so long as the battery ends up around 13.4-13.6 volts it’s fully charged.
Every lithium battery is a little different. If you want to know the exact charging voltage of your specific lithium battery, you’ll find it in the product manual.
Final Thoughts on the NOCO Genius 5
Just to sum things up, the NOCO Genius 5 can charge lithium-ion batteries so long as they have a built in BMS and aren’t over 120 amp hours in size.
But if you want to keep the Genius 5 safe and in good working condition for a long time, I don’t recommend using it to charge a lithium battery regularly.
It’s also going to charge the lithium battery slowly.
For every other kind of 12 volt battery and flooded lead acid 6 volt batteries, it’s one of the best battery chargers out there.
Have any questions about charging lithium batteries with the NOCO Genius 5? Leave a comment below.