Rebuilding B&D Pivot Vac Battery, Cell Questions

majerus

New member
Joined
Jan 15, 2021
Messages
4
I am trying to rebuild the battery for a hand vac that died within 4 years of very little use. (Will only run for about 2 mins) So far I have taken the 18650s out (LGDAHB71865) and am looking for a replacement cell that might increase run time and overall last more then a few years.

1) Couple questions, did the cells likely die due to a crappy BMS that is on the battery pack?
2) When replacing the cells what is the most important specification to match? (I am thinking Max Discharge Current, and charging type?)
3) This cell has a label of LGDAHB71865, however I can only find a model that is similar IMR18650HB7 are these effectively the same?
4) Is there a go to cell for this type of application?

Thanks for the help!



 

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kc8adu

Member
Joined
May 22, 2019
Messages
105
they are a 1500mah 15a continuous cell. and probably old age and an application that dumps them in about 5 minutes.
i would replace with these.
those are my go to for tool pack rebuilds.
just rebuilt some porter-cable 20v packs with them.
btw porter-cable packs are the same as black & decker except brand lockout tabs!
i gave the rebuilt packs their first charge on my black & decker charger.
 

majerus

New member
Joined
Jan 15, 2021
Messages
4
Awesome! Ill pick some up. Brand lockout tabs? Just talking about the battery connector?
 

majerus

New member
Joined
Jan 15, 2021
Messages
4
So the batteries after running them through the LIItoKala Engineer LII-500 NOR test show the following results.

1) Cell 1 and 2 are clearly bad due to their low mAh rating right?
2) Looking at this data why would cell 3 show 3.85V after testing, and such a large capacity does that seem odd?
3) Should the voltage of all the cells be so varied after the test ran?
4) Anything you see in these testing results that can help a noob understand what the state of these cells are?

I am going to buy all new cells, however want to understand the process as I might one day try to build a pack, or diy powerwall.

CellVoltsCapacitymR
14.20314 mAh101
24.00935 mAh55
33.851153 mAh62
44.121276 mAh55
54.211109 mAh124

1611295104292.png
 

ajw22

Well-known member
Joined
Nov 16, 2018
Messages
584
Decreasing capacity (mAh) and increasing Internal Resistance (IR, measured in "milli-Ohm", and sometimes written as mR) over time and charge/discharge cycles is natural and unavoidable. IR measurement can be quite inaccurate on these chargers, esp if the contact is bad.

While a small drop in voltage over time is expected, significant voltage drop over time indicates a more serious defect ("self-discharging cells"), basically a partial internal short circuit. It seems(*1) cells #1 and #5 are fine in that regard. Cells #2,#3,#4 are self-discharging at high rates and should be considered defective. Particularly #3 is so bad, you might feel some heat coming off the cell.

(*1) Normal approach is to let the cell sit for a couple of weeks, so that any self-discharging becomes more obvious.
 
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