Surely the threshold current depends on whether li-ion or NiMH, because more heat is produced at the higher voltage for the same current level?
FYI, I end up buying the Vapcell S4 Plus from 18650 Battery Store, and it arrived yesterday. So far I am VERY underwhelmed with how this charger handles well-used and/or older NiMH batteries. 
I will report more after further testing…
Darn, that’s disappointing to hear. Maybe you’ll have luck with the reconditioning feature?
I used for both.
However, I only checked capacity mAh for li-ion batteries that I had from old laptop pack.
So I do not know how well it performs for all battery types.
But overall, I am happy with it, will probably by a 2nd one a bit later in the year.
Yes, I also have not seen HJK-style reviews for this thing, only end-user/anecdotal experiences such as mine.
Until my lii-500 emerges out of the Covid fog I am using a folomov a1 and my old Great Planes Triton lol. It can cycle and discharge to 3A but if course just one cell at a time. It was only intended for battery packs.
I have tried the Repair feature — as well as all the other modes. On most cells the charger only charges them for a few minutes at most to get to 100%. Then it discharges (the supposedlyy fully charged cell) in just seconds. Perhaps the batteries are the issue? Once I have tried more cells, I will report back with my thoughts — but at this point I get the impression the Repair feature won’t really do much at all for NiMH cells.
So you have used your Hohm Tech Base 4 to charge both NiMH and li-ion cells, but you have not used the Battery Doctor feature on any NiMH cells — correct? If you have any old NiMH cells perhaps you can see what that Battery Doctor feature can do for them. 
After using it with more cells and switching to Manual, I think the issue is the Repair mode always discharges at at least 500mA. My older cells must not be able to handle that rate so they just quickly ‘discharge’ — except they aren’t really being fully discharged like the charger thinks. When I try the charger’s Discharge mode and set the current to 250 mA, then I am seeing the results I had expected. It’s really pity that the charger doesn’t give the user the ability set the discharge rate in Repair mode (and 500mA is the lowest it uses)!
No, not correct.
Sorry I was not clear.
I used battery doctor on both li-ion and nimh.
With battery doctor on li-ion, I have gotten one cell repaired (I could not get more than 300mah before, now I can get over 1,300)
and the other went up by about 500 mAh (although I lost the record of exact numbers).
What I meant to express is that I did not record the capacity improvement of nmih cell.
If AA won’t handle 500mA discharge, it’s kind of pathetic. You may have a bunch of junkers.
Mind you, I have some and do use them for some small LED applications. I’ve found I recycle for sure when AA won’t handle 300mA discharge, or show other issues.
Thanks for clarifying!
One question about they above statement, does it mean you didn’t get any improvement (using Battery Doctor on NiMH cells) or that you just didn’t make note of any of the numbers when you did it?
I searched my old emails to find out the AA cells I am testing were purchased in 2008! My newest cells are from just 2010 — so it’s time to invest in some new AA rechargeables. I will probably pick up some from Ikea once things reopen.
I am still testing my old cells because I want to determine which ones can still do 250mA because from what I understand they should still be useful in remote controls and in things like LED candles. I have tested four so far and 2 couldn’t even handle 250mA but they other 2 could and are measuring around 1300mAh. They were originally 1900mAh LSD cells, and from what I read about older, worn cells should still retain their LSD properties.
I just didn’t make note of any of the numbers when I did it.
Okay, thanks again.
I am doing some testing now. Surprisingly my 2010 cells — which are Rayovac 4.0 LSD NiMH rated at 2000mAh — are looking pretty decent according to the charger’s Capacity Test mode. It is reporting capacities of 1600-1800 mAh. Once the Repair mode concludes I will see if capacity is increased at all.
The 2008 cells I started testing with — which are Nexcell’s EnergyON LSD NiMH rated at 2000mAh — are looking pretty worn out. Many cannot even handle a 250mA discharge, but a few will (but not a 500mA discharge). Those test with capacities of 1100-1400 mAh. Since the Repair mode does a minimum of 500mA discharge, I am not able to try that mode on them.
Are the Rayovac 4.0 blue and silver? I have a bunch of those, mostly 2010 and 2011. I’ve beat the hell out of them. None have died, a few are kinda lame, but most are still decent. I’m shocked.
I’d had some Nexcells. Not good, at least the ones I had. Don’t remember the specific model as they are gone now.
Yes! Once I realized just how old they are I was quite surprised too! I got mine for a steal too; I bought 16 AAs and 8 AAAs all for just $37 including shipping back in 2010 which was crazy cheap back then (and still looks good today).
Mine are all white with blue lettering that says energyON — so they were trying to look like eneloops. They were bundled with a LaCroose BC900 charger that I bought from Thomas Distributing back in 2008. None of buttons on that charger work anymore, but it can still charge individual cells at 200mA (the default setting).
I tested two of those Rayovac 4.0 AAs using the Repair mode of the Vapcell S4 Plus charger, and neither gained any capacity — in fact both appeared to lose a little. Using the Capacity Test mode one measured 1757mAh and the other 1670mAh. I then did the Repair mode, then after that did another Capacity Test. This time their numbers were 1720 and 1632 respectively. After that result, I do not plan to run Repair mode on any of my other Rayovac cells as long as they measure out with a capacity of 1600+mAh.
I should mention one issue with the Capacity Test mode on this charger; it only partially recharges NiMH cells after the discharge part of the test. So when it shows they are done and ‘fully charged’ you need to kick it over to Charge mode to really get them full. HKJ saw the same issue when he tested this charger.
I got a VC4 in the mail, so far it is charging great but I was under the impression that I would be able to select the charge current. I will just have to be mindful which slots I put the smaller 16340 cells in since I cannot adjust that. So be more careful to read the specs and maybe even the manual before you buy.
The Xtar VC4, VC2S, VC4S, and Allmaybe(Xtar) TC2 doesn’t appear to support changing the charge current.
(in particular, the VC2S and VC4S seems to be aggressive (high charge current) in auto-selecting the charge current if it’s a low-resistance battery but doesn’t know it’s a small-size/capacity battery)
Only some bigger chargers, like the Xtar VP4C, Xtar VC8, Xtar Dragon VP4 (and maybe a few others) support changing the charge current…
I also have a XTAR VC4. My main reason for buying was to get a quality charger that supported both li-ion and NiMH for cheap (mine was only about $15 shipped). As you said, you can select 500 or 1000mAh based on which slot(s) you use. I wanted more control — and more modes/measurements — so I recently bought a Vapcell S4 Plus.