Darfon Gro Watt GBLI 5001 Battery Pack- worth a punt?


New Member
I've been offered this - seller is fair and flexible, price is somewhat dependent on how useful it'll be for me.


I can't get any sign of life out of the BMS, but that's likely due to the string voltages. Took out one row and this is what they measured at:


It's using these Boston Power Swing 5300 cells, which from what I've read are pretty good when new.

As the cells have been discharged well below the specced 2.75V. Is there any hope for them?

If they're likely to be usable or revivable, I'm thinking of reconfiguring it as 24V (my main inverter is 24V) and using a different BMS, as from what I've read the main weakness of these systems is the standard BMS. If that sounds sensible, does anyone have any recommendations for a suitable BMS?

Or should I just walk away?



Offgrid Cabineer, N.E. Ontario, Canada
If it is REAL CHEAP I'd consider it.
How long have they been below cutoff ? The longer it has been the loss of capacity will increase.
Can they be salvaged ? Possibly, only one way to know, is a nice gentle charge to 3.0Vpc and then observe & measure over a few days to see how much settling occurs from 3.000V per cell.
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New Member
Thanks- I meant to say that he's not sure how long they've been sat for. I'll see if he can find out- he does seem to know the original owner. Info so far has been vague, other than it was installed in an attic and upgraded a while ago.

I'd like to give charging them a try. My issue is with how best to do that. I have these at my disposal:
  1. I have a bench power supply, it's only capable of 3A, up to 60V. Is it worth giving it a try with that? I realise it'll take a while. I'm guessing it'd be best to charge each string individually if using this, rather than sharing those As across multiple strings?
  2. I have the APC UPS that you can see in the top photo. I believe it's working, but the set of VRLAs was dead when I got it. That runs @ 48V- I'm imagining that the voltage of this pack will be too low for it to even start charging...
  3. Some regular Li 18650 chargers that can do up to 1A per cell- could I use those somehow?
  4. A 3.5 kW 24 V Studer inverter/charger that I could connect to the mains. This is highly configurable as far as charging current/ voltage etc.
  5. A few different regular 12 V car LA battery chargers
Or none of those any good?

Could well be real cheap, price will depend on the results of the testing, if I can get them charged : )


Offgrid Cabineer, N.E. Ontario, Canada
1st things 1st... All Lithium batteries are FINICKY and each chemistry has a different voltage curve, limits etc... car chargers or chargers for ANY other chemistry is a risk at best to foolishly dangerous. Even Will Prowse had misadventures (costly ones too) with the wrong charger.

Stored in an Attic ? WTF !!! LAST PLACE IN THE UNIVERSE to put batteries, especially ones that are Temp Sensitive ! Especially Hot Temps. And they wonder why the pack died. IF it was me and that was told to me, I'd continue walking as those lived in a highly abusive environment. Believe me when I say, that ALL Lithium loves the same temps as the human being does while wearing a T-shirt & pants, not too hot and not too cold. I'd give him $50 just because of the parts & bits and the possibility that some cells may be OK and only if I was feeling generous. Sorry, not what you hoped to hear I bet, but it's my feeling & opinion.

Now, I CANNOT identify those cells, I do not believe they are LFP (LiFePO4), you MUST know what the chemistry (no guesses) is before attempting to charge them. There is 14 packs of cylindrical cells from what I see, they "could" still be LFP but the specs you posted are not clear on this, there is some odd values if LFP.

Because it is Cylindrical Cells set into "packs", the cells are most likely welded to their busbars internally, the packs likely "may" be separated from each others but depending on how they are interconnected will determine how best to do so.

The BMS is likely in Protect Mode due to undervolt and so won't initialize. (normal behaviour for safety) Often there is a reset to allow it to operate IF charge voltage is present. Every BMS is different, so we would need to know the make, model & version of it and MAYBE info can be found.

The Bench supply if set to 56V/3A may be slow & very gentle but likely the best way to see if they'll come back up IF the BMS can be reset. With that there would be no risk of overcharge at a high rate. FYI NCA, NMC "Li-Ion" chemistries form dendrites in Lo Charge State which can lead to internal shorts & worse.


New Member
Thanks all- I've got the ability to play about and test them without making any commitment, so I might as well try.
These were in the south of England- there aren't much in the way of temperature extremes here, so maybe the cells won't have been affected by the temps. But the low SoC for a currently unknown length of time (i'm going to try to get more info on the history) is more of a concern to me. The fact that these have an unusually wide operational temp range (-20 to +60 °C) gives me some hope for them not having been too affected by temperature in their installation location, which is unlikely to have been outside -5 to +35 °C.

The cells certainly seem to be good spec. I thought I'd linked to this previously, but see that didn't work... This is the link to a pretty lengthy discussion about them, with mostly favourable reviews: https://endless-sphere.com/forums/viewtopic.php?t=90938
They aren't cylindrical. Rather than 2 cells together, they're actually 1 cell that's oval wound. There's a video here of a guy cutting one open (I've started it where he's cut it open):
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New Member
A rather belated update on this back-burner project...

I bypassed the BMS and charged the battery very slowly (3 A across all cells until system voltage reached the specified 57.4). This took a long time as I have not been able to get to my workshop much and I did not want to leave it charging while I wasn't there keeping an eye on it.

All cells came up in voltage very evenly, other than strings 7 & 8, which started at lower V so by the time the battery was at the 57.4 V, these 2 were considerably lower than the others. I found that these strings are not monitored by the BMS. There aren't even monitor wires going to these cells. I've never seen this before, seems very odd to me.

I was impressed with how balanced all of the strings other 7-8 remained during and after charging. All within a few hundredths of a Volt.

Once I'd realised the situation with 7 & 8 & how far behind these strings were, I charged them separately to bring them up to the same voltage as the rest- I inadvertently let them get to a slightly higher V than the other strings, but the maximum they reached was 4.098 V.

I then took a measurement of each string each time I was back at my workshop. The results are below. (The 2 high strings are 7 & 8, which were charged separately).

Initially there was no sign of life from the BMS. I tried again once it was up to voltage. The LED flashed green for a second, then went red. There was no output. I tried long-pressing, double-pressing... There are no marks on the PCB, it appears to be made by Darfon. My guess is that the BMS died, which is why the battery was decommissioned. I have read elsewhere that the BMS in these was not reliable and tetchy old tech.

So my question is, based on these results, the batteries being specified for use in a wide temperature range, the fact it looks like the BMS went bad, the cells seem to be OK considering their age, and that I'd likely be able to buy this for a very good price (that conversation with the owner still yet to be had- he's awaiting me making him an offer), do you think it would be worth buying a new BMS and giving it a go? I guess the only sure way of knowing if they're any good is to try them with a load over a period of time and run them through a few charge/ discharge cycles.

If so, what about converting it to 24 V? Reason being that I have a 24 V, 3.5 kW inverter that I could use this with. The only 48V kit I have is an old APC PSU. It has copper plate interlinks and 10 mm cable between the cells. Would I need to upgrade this? Otherwise, it would mean finding a used 48 V inverter charger and charge controller for a decent price.

Unless these results are ringing alarm bells for anyone, I'm tempted to spend a bit of money to see if I can make use of this. The cost to buy it is likely to be very reasonable, but what would you offer for it considering these results?

Many thanks


The system voltage