Sunday, June 18, 2017

Lithium (LiFePO4) Battery Charger Review and Comparison: OptiMate vs CTEK vs NOCO Genius



A while back I did a review of a lead acid battery chargers that has been one of my most popular posts, so when I needed a new lithium battery charger I decided to do another review and test. Here it is!

Some background on lithium battery chargers

I've been using lithium-ion batteries in my motorcycles lately.  Technically, these are lithium iron phosphate (LiFePO4) batteries  These are also sometimes called LFP batteries (and sometimes incorrectly called LiPo; this a slightly different technology). For ease, I am going to call them "lithium batteries" in this article.

I have both Shorai and Antigravity brand batteries in my bikes. And as it happens, I had two bikes with lithium batteries in storage for more than a year. Neither bike is in "running condition" so I thought it was time to charge their batteries.

Now most people may never need a special charger for these lithium batteries. If there is no drain on them, they can go a LONG time without charging (probably more than a year). So don't run out and buy one of these special chargers unnecessarily. If you need to leave your vehicle for more than a week or so, just disconnect the battery and don't worry about it, even for months.

Shorai publishes a nice chart of showing how you can use your battery voltage to estimate much charge your battery has left:

And if your battery charge does get low, Shorai explains how you might be able to charge the battery with some "regular" chargers here: http://shoraipower.com/charging. Note that you can NOT hook a lithium battery to a just any lead acid battery charger and forget about it! You need the right kind of charger and it is a careful procedure, read and follow the directions.
More detail on the problem using a regular lead acid charger with a lithium battery: Many or most electronic type lead acid battery chargers have a "desulfation mode" which cannot be turned off.  That mode will damage a lithium battery! Also, the final voltage for a lithium battery is different (higher), and a regular battery charger will not handle that.

Now, probably the THE BEST way to charge a lithium battery is to get a special charger with a Balance Management System that can charge the battery through the "Balance Connector", if the battery has one. This allows each individual cell in the battery to be "fully topped off". The Shorai does have a balance connector and Shorai sells a special charger for that port. If you want to buy a specialized charger like that, it's probably the best way to go!

On the other hand, many brands of lithium batteries do not have the special balance connector. Some of the manufacturers claim to have have a built in cell balancing circuit (EarthX is one). Others claim (like Antigravity) that it isn't necessary, and some just don't say anything.

Another feature of some lithium batteries is an "over-discharge protection circuit". If the battery is in danger of being drained too low, it disconnects the actual internal battery from the terminals on the battery's case. If the battery has triggered the protection, it cannot be charged until that protection is reset, this is often called "BMS reset". If the battery is not reset, the charger does not recognize that it can be charged. The manufacturer EarthX describes this well on their website.

What do I want in a lithium battery charger?

Because some of my batteries do not have balance connectors, I wanted a a charger specialized for charging lithium batteries without a Battery Management System that requires the special connector. A lithium battery charger should work using somewhat different charging steps and voltages and should definitely not have a desulfation mode. The charger should also be able to reset any over-discharge protection circuit inside a lithium battery.


The Contenders

A little research showed 4 chargers that interested me in the US$50 to US$100 price range on Amazon. Here is a list with the manufacturer's web page for each and also a link to the manual for each:

Noco genius G3500 3.5 Amp UltraSafe Battery Charger and Maintainer

User Guide
(about $60 on Amazon as of this writing)

Frankly, I wasn't thrilled with the regular lead acid Noco charger I checked out back in 2012. But I thought I should check them out again.The G3500 is a fairly hefty 3.5A charger, so that was good. And it is a multipurpose charger that works for lead acid 12V and 6V batteries as well as 12V lithium batteries. They claim "8 modes" in the manualbut I think this is a bit of over-marketing. For instance, one of the 8 is "Standby" which is essentially "Off".  Regardless, it will work with multiple battery types, and if that is useful to you, that is a good thing.
But I was evaluating how this charger would work for Lithium batteries and I found some things I didn't like. The manual claims an 8 step charging sequence... but it doesn't say anything about how it works differently, if at all, for a lithium battery. Perhaps the charger's lithium mode just skips the desulfation step and ends in a voltage appropriate for lithium batteries? There is no way to know. The manual also doesn't describe any way to reset the BMS on batteries that have that built in.
So... I rejected the NOCO and I did not buy one to try it.

tecMate OptiMate Lithium 4s 0.8A TM-471

User Guide
(about $60 on Amazon as of this writing)

The OptiMate Lithium comes with lots of great recommendations. At least 3 of the battery manufacturers recommend or resell OptiMate chargers: Antigravity, EarthX and Ballistic.
So I ordered one of these up and checked it out.

Sadly, I found the LEDs hard to understand. Even with this key from the manual it isn't perfectly clear:

Here is what the manual says about LED #5 and #6:
VOLTAGE RETENTION TEST: LED #5 flashing Delivery of current to the battery is interrupted for 12 hours* to allow the program to determine the battery's ability to retain charge. For batteries with a good state of health LED #5 (green) should continue to flash for the full 12 hours* period. Read the section NOTES ON TEST RESULTS on reasons for poor test results or how to test a battery that returns a good result but cannot deliver sufficient power once it is returned to service. 
MAINTENANCE CHARGE: LED #5 / 6 steady on For 30 minutes the circuit offers current to the battery within a safe 13,6V voltage limit whilst the result of the voltage retention test is displayed. If LED #6 (red) indicated the VOLTAGE RETENTION TEST will be repeated. A steady LED #5 (green) indicate the 30 minute float charge maintenance periods follow and alternate wih the 30 minute REST (no charging) periods until the battery is disconnected. The battery can draw current as required to support small loads and counter self-discharge.
Is that clear? It means that LED #6 will go solid green when the charging is completely done.
But note what the manual says about the "Voltage Retention Test", LED #5. It says this test lasts for 12 hours! And guess what... it wasn't true; when I charged my Antigravity battery (which wasn't badly discharged at 80%) the "Voltage Retention Test" alone went on for MORE THAN 24 HOURS (this is in addition to the time required to charge the battery before this). And note, this is a relatively low powered charger, at 0.8A, so it isn't particularly fast anyway.
Now, I really like the idea of this test. And obviously, you could just disconnect the charger before this test is completed and use it. But I was annoyed by the strange LEDs. This charger should have the LEDs all in a row like the other brand chargers, and a clear indication when the charging is DONE and then a clear indication the 24 hour charge retention test is happening. 

Also, while some Optimate chargers can reset the "over discharge protection circuit" on some batteries, it is not clear that this charger has that feature. It isn't mentioned in the manual but the website does say it has this feature. It would be nice to mention the feature in the manual if it is included in the device. I think it is probably in there...?

In summary, I wasn't thrilled with the OptiMate charger.

CTEK (56-926) LITHIUM

Manual
(about $80 on Amazon as of this writing)

Here is what came in the box:


The CTEK is a lithium battery charger only and charging steps are clearly described in the manual. There is also a linear array of LEDs on the charger that clearly show the progress of the charging.
Check out these two pages from the manual:



Perfectly clear and concise! So refreshing after the OptiMate manual. Note how it clearly shows how to reset the "over discharge  protection circuit" in a battery that needs that.

The unit itself is handsome enough. I do wish it was rubberized on the corners to protect it from drops and some rubber feet would be nice too. It does look like it will become scratched and worn over time. But note the nice and simple LEDs, the clear reset button, and the voltage and current rating right on the front.


Here is a closeup of the LEDs:


The manual page above clearly indicates which steps/LEDs indicate the battery is "READY TO USE" (step/LED 3) and "FULLY CHARGED" (step/LED 7). Tip to CTEK: This really should be printed right on the label, there is plenty of room! I may add a sticker to mine as a reminder.

So I tried the CTEK on my Shorai battery, and it worked fine. The battery was at about 85% charge when I started it, and when I went back a later it was fully charged. No problems and easy to understand.

Conclusion

My choice: The CTEK Lithium charger. It has the most clear manual and good LEDs. It clearly states that it can reset an "over-discharge protect circuit" and has a button for that feature. The manual clearly describes how it's steps work on the lithium battery, including the voltages used and how long the steps should take.

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