My Xtar VP2 will overcharge

Are you measuring things with a quality volt-meter?


And is the DMM battery still good?

The display voltage, multimeter, and Anduril voltage display agree.

Let me get back to you later after I review this further, but I think from the discussion I’m beginning to understand what you’re seeing - but unfortunately, not what’s causing it (root cause). Here’s something to consider for now. If you’re seeing what you indicate, and I understand correctly, your charger is indeed likely overcharging (too high voltage), and I’d recommend you stop using it until you get it sussed out.

It sounds like your charger is indeed charging to an incorrect CV value which is much higher than the correct 3.6V, and is likely exactly what your voltmeter indicates. If it is higher than 3.6V, which it should NOT be by any significant amount, the VP2 will not show the correct value - it will only show 3.6V, although your voltmeter certainly will and apparently does.

The key is this: Go back to your LYGTE link to the test / review, and I think you’ll see why after completion of the charge cycle, what you see on the VP2 display, and what you see if you check the batt voltage w/ your voltmeter do not agree, and it’s apparently because the charger is exceeding the correct CV phase voltage. Here’s the key text:

The voltmeter has a good precision, when charging it will show slightly above the battery voltage, as expected. Sadly it will not really work above max. charge voltage: it will show one value and then stop updating.

So, if it’s overcharging (voltage), you will not see it on the VP2 display, but will only see it with your meter. Believe the meter, because it will be the correct value. Good thing you have one, just for situations exactly like this one.

So that only leaves the question of why your charger is charging to CV value approprate for a 3.6/3.7 V chemistry cell (which is 4.2V), instead of the CV value appropriate for your 3.2 V (LFP) chemistry (which is 3.6V). If so, it’s a serious malfunction of the VP2, which is why I recommend not using it at this point.

Given that text from the review (thank you LYGTE), this is starting to make sense to me. It probably means your charger has a fatal problem, which is not good news, but at least it’s making sense.

Is this making sense to you too, or is it just me:-)

It makes perfect sense, thank you.

I noticed that my VP2 did not have that yellow anti-counterfeit sticker that’s pictured in the review thread (Test/Review of Charger Xtar VP2). Maybe mine is a fake. Illumn might want to know about that. I’m bringing this up with them first, and will check with Xtar if they don’t have an answer for me.

I’m actually watching / noting some numbers on a charge right now, and will have a few further comments at some time, but that stuff is all academic at this point Your observations noted in your posts have essentially proven that your specific VP2 is defective (which is rare, it must be said), and LYGTE’s excellent (and important) observations I quoted above have determined exactly why what you were seeing was (justifiably) confusing (due to a design deficiency that your failure exposed in the VP2), so you’re ready to take action on the charger resolution. You have all the information anyone you excalate to should need - unless they want photos or something). Again, I would not continue using that charger at this point given what you’ve seen.

Yes - Both of my VP2s DO have the yellow stickers on the front which appear to be the same as the one pictured in LYGTE’s test. Its absence on yours is questionable I guess. Just FYI, I purchased both of mine ~5 years ago from Battery Junction.

Anything can fail. That said, anecdotally I don’t recall hearing of any serious failures with VP2s - primarily just dimming of the displays over long periods of heavy use. Perhaps a non-critical failure I’m forgetting, but the falure you’re seeing is what I consider a “serious” and “critical” failure (one that can cause further damage). That said, it may sound crazy, but in your situation I would still consider replacing the failed unit with another properly-functioning VP2 - and that would be underscored further if the authenticity of your unit proves to be suspect.

Again I’ll follow up a bit on this, but you pretty much know what you need to know to deal with the unit you have.

I hate to tell you this, but I just noted that some sort of malfunction happened with one of my VP2s tonight while I wasn’t paying attention. It may be similar to the overcharge problem you observed, and is nothing I’ve seen before. Mine appears to have over-charged a cell that I left in the unit unattended for quite a while following a normal charge cycle (knowingly), and when I started to put things away a few minutes ago I just noticed it. There may be more to this than I thought, and it’s possible that your unit may not be just an isolated failure, and one of mine may have exhibited a similar failure - which means this could be a design issue here rather than a one-off failure as I thought. I’ll be investigating further, but for now, be aware that there could be more to this story than just a single failure with your particular unit. It doesn’t change what you saw or the failure you experienced, or your efforts to possibly get your unit replaced, but the issue may go deeper than that. Obviously more testing is now required on my chargers, and I’ll let you know what I find. If what I think happened actually happened, I may be looking for a replacement for both of my units - which of course isn’t good news:-(

I have a Nitecore D2 charger that does LFP somewhere. I plan to test that in the same way next. Hopefully you, I, and that unfortunate fellow with the UMS2 in the other thread aren’t in the process of uncovering an industry secret that LFP charging mode in consumer chargers is complete BS.

It seems unlikely, but then again a host of otherwise very thorough reviewers never talk about what happens when they leave cells on a charger, because that’s not something anyone recommends.

You may want to ‘hang loose’ on this, as I think I may know where this VP2 train is leaving the rails, and the VP2s may remain usable for us as long as we adhere to ‘best practices’ - meaning the problem may be both predictable and avoidable. You may not want to escalate this functional issue regarding yours, as it may well be ‘in the design’; however if you believe your example may be a ‘fake’, you likely should escalate that issue, which in my opinion would be unacceptable. I’ll do some testing since I have 4 cells I don’t mind sacrificing, and will follow up with additional info which has come to light (as a result of re-reading LYGTE’s excellent test results even more closely). BTW - those referenced Nitecore charger issues sound unacceptable to me.

Update: illumn is pulling some samples from stock and testing on them.

Weird. Xtar chargers have Been reliable so far with no issues

Just checking, are you saying your VP2 does not do this?

fran82 -

There could be a little ‘group think’ involved, which is insidious and can thrive in forum environments - and like rust, it never sleeps, and without intervention can keep growing.

It’s also a mistake to assume that a company which builds a number of great products necessarily builds ALL great products. All too often, that is not the case, and it’s best not to generalize.

Keep in mind that the VP2 was likely designed almost a decade ago, so there’s that…

Lastly, and in this case probably most importantly, some otherwise great products may have a single, serious problem which may only be evident in ‘edge case’ situations and thus may be only rarely seen by a few users. The jury’s still out on this one (but not for long), and at this point I suspect this is the situation that applies here. Stay tuned…

Achilles’ Spiel -

Testing - one - two - three!
I’m doing the aforementioned testing, but as you well know, testing for this problem takes a good bit of time. Stay tuned, and I really expect that a definitive, conclusive answer regarding this issue will be forthcoming this weekend.

Just send it back in and buy another one, or not.

It’s not functioning correctly.


I get you Chris. Aside from the OP’s unit however, I’m very interested in my two units which I currently use daily for something. If there’s ‘fatal’ problem that can bite me hard - I want to know about it, and what it is, and when it happens (if possible). I could just trash both of mine at this point (and it’s tempting), but I wouldn’t know what to replace them with (and any suggestions in advance would be appreciated:-). I’m testing so I can make a judgment about what to do with my two units. I’m pretty sure I understand it now, but I’ll wait until that’s proven in a while. If it’s what I suspect, and if you do LFPs on yours, I can assure you that you will want to know about this too.

Would be nice if it were that simple. The VP2 is the only one I have found that doesn’t require a separate action to charge LFP cells. Drop in and go. I don’t want it replaced with another defective one.

My tests are still in progress, but if they end as I expect……

Here’s a little preview of what I think I may be ordering soon:-)

Don’t laugh. K2 makes great cells that I use, but just as important, LFP stuff isn’t just a distraction or niche sideline or charger spec for them; it’s a core part of their business (check their site). I’ll bet they’re quite capable of building a purpose-built / dedicated charger that’ll do a fine job of properly charging my LFPs without worry, and 16x34 is the only size LFPs I use, so…….

EDIT: If I’m guessing right, other chemistries may[ Edit insert:] ‘not’ be an issue for the VP2.

achilles’ spiel I have not tested or tried the following. So, take it for what it’s worth.

In my thread:

Gun Light, CR123 or CR2, Need LiFePO4 EXACTLY 3.25 V - 3.30 V

Jeff51 mentioned using the idea of a simple power supply to charge batteries. He mentioned this product from DROK.

Again, I have not tested the theory or the product. I have some DROK products I like and some I don’t. This is an inexpensive unit. It’s not going to have super advanced safety features or warranties. I know from the description that the voltage resolution on that unit is 50 mV. That probably means on the display. But, as jeff51 in the other thread said, you might be able to calibrate it with a voltmeter. So, if you calibrate the current to 1/2 C or whatever relative to your batteries and the voltage to 3.7 V, you might be able to just attach a battery and let it run. I would never leave it unattended and you might need to keep a voltmeter attached for precision measurement. I linked to some battery holders in the other thread that allow attaching to CR2 or CR123 batteries.

I don’t know if this is a better option than what you have, but it might be ONE option.


I have 2 concurrent, but staggered tests running on my two VP2s which were started last night and which I want to continue to let run for a good while yet. I’m charging one LFP 16340/123 cell in the left bay of both chargers. At conclusion of my tests I’ll have most of the info I want, but also want to check some other things when the chargers are available again. That will take me through this evening, but because I currently already have most of the info and answers that most people will likely be most interested in, I’m posting a summary of pertinent facts and data now, and may follow up with more info later if appropriate / desired.

Both of my VP2s are behaving similarly, and both exhibit essentially the same over-charging malfunction noted and described by the OP in his posts. This suggests that the malfunction is not the result of a defective unit, but is rather the result of a design issue.

If left unattended following normal termination of a charge cycle (status LED turning Green) using LFP cells, the chargers will ultimately ‘overcharge’ the cells to a significantly higher voltage than the normal 3.6V CV parameter appropriate for the ‘3.2V’ (LFP) switch setting. I currently show >4.1V on the first of mine, with the second following suit, and the OP measured 4.2V on his. I’ll find out how high it will ultimately go, but it’s already well exceeded ‘unacceptable’. Note that as previously mentioned and verified by the earlier HKJ quote in an earlier post, at this point the VP2 display will only indicate the rising voltage to 3.6V, and after that it must be monitored / checked with a voltmeter.

The initial charge cycle appears normal and proper in every respect up to the ‘green light’ status indication / termination point. The cell voltage then decays / settles in the normal way for LFP cells (and is reflected accurately on the the VP2 display). The malfunction is ‘triggered’ / precipitated at a point which appears to coincide with this ‘feature / bug’ referenced in HKJ’s test report which I’ve copied here:

“Charge will restart if battery voltage drops to 3.9 volt (3.3 in LiFePO4 mode).”

Note first however that this function appears to start at a display-indicated (and accurate) voltage of ~3.36 - 3.37V, not at ‘3.3V’ as stated. The actual point can be determined by observing when the indicated cell voltage hits a ‘floor’ and ceases to drop slowly, and instead begins to slowly increase. If you watch the LSD of the display, you’ll see it - and that’s the only indication you’ll see. Also note that this ‘restart’ of charging in no way resembles a normal ‘restart’ of a charge cycle as one sees when, for example, removing and reinserting the cell. It is not indicated to the user by the status LED, as that remains Green throughout this process. I also does not appear to use any normal charging algorithm (which would start at CC and determine the SOC (state of charge) of the cell. It is seen as simply a very slow ramping of voltage from that trigger point and continuing for many hours until the proper CV value has been far exceeded. The unit appears to be ‘out of control’ and in some invalid (and certainly improper) state.

If a user charges LFP cells and adheres to best practices and removes the cells in a short amount of time following charge termination, no problem should be experienced. Unfortunately that period of time is fairly short with LFP (where the voltage decays more and more rapidly than most other chemistries after charging termination), likely varies with different cells, and is therefore difficult to predict. Within an hour of charge termination, one could be in the ‘danger zone’. One can probably get away with a delay of 1/2 hour, but there’s no guarantee. The only guarantee is that it is unforgiving, and without intervention will malfunction and overcharge the cell(s) at some point. Again, you can watch the VP2 display and determine this yourself using your cells.

I haven’t fully tested these specific conditions using 3.6/7V chemistries, and do not know if the malfunction would be likely to be encountered in normal use with those cells and the 3.6V switch setting. Given the ‘3.9V’ number for other chemistries implied in HKJ’s note above, I think it would take a very long time for any of my such cells charged to 4.2V to ever decay / settle to that value, so it may effectively be a non-issue with such chemistries. In that respect the malfunction may in practice be effectively (if not specifically) LFP-specific.

Let me know of any questions you may have, and if I have answers I’ll share them.