Back in the early 90s I worked at a place that had a small warehouse full of UPSs, many of which had sat around for 4 or 5 years just waiting to be sold. They had 12V 6.5Ah and 24Ah batteries that typically measured about 2 volts. They would put new batteries in them before they were sold, so I had way heaps of batteries to experiment with.
The technique was refined to the following:
Reverse charge the battery at 2% of its Ah rating for 48-72 hours.
Then forward charge the battery at the same rate, again for 48-72 hours.
Absolutely under *NO* circumstances crank up the charging current!!! If you do, you will find one cell will get hot and then it’s all over, red rover. It’s junk.
Recovered many batteries that way including one 24Ah that I put in my Daihatsu Charade and it would easily crank it for several minutes continuous. Didn’t try to see how long till it quit.
So it can be done with batteries that were once good but just sat around for a long time, but as for old worn out batteries, I don’t think so.
I've just got the perfect candidate to try this ^ !
A 12V MOTOBATT AGM 20AHr
http://www.motobatt.com/MBTX20UCCA 310A, Capacity (10HR) 21 AHr
~3years old from a neglected jetski score !
Free standing open circuit voltage 1.7V
A previous quick look at this battery a few days ago to see if it would take a charge was done with a reasonably modern LA charger that needs a residual voltage before it will charge and of course this battery wouldn't. Another dumb LA charger was connected also to bump the voltage up to where the smarter charger would latch and commence charging but when removing the 'bump' charger, charge was not maintained.
Normally I'd give this one up as stuffed but the case looks perfect without any swelling/bulging.
Circlotron battery recovery method.Started NZ time = ~10pm 26 Nov.
2% x 20AHr =400mA reverse charge from a CC supply set to 13.8V, CC'ed down to 1.6V......will this work ?
Will check it several times/day and make any necessary adjustments if/when required.
Supply: MCH K305D (30V 5A SMPS) All charge voltages and current noted from the PSU display readout.
Discharge voltage and current measurements: Fluke 15B and Kaise analog meter.
The clock is ticking !
Reverse charge progress log:ALL charging measurements .....PSU set to 13.8V and in current controlled (CC mode)
Measurements from PSU display readout unless otherwise specified.
0 hrs. Voltage 1.6V @ 400mA
reverse charge.
10 mins Voltage 1.4V
15 mins, Voltage dropped another 100mV to 1.3V.
20 mins, Voltage 1.2V,
2 hrs. Voltage 1.0V, Battery cool to the touch.
7am 27 Nov
9 hrs. Voltage 1.0V. Current 400mA stable and battery cool....no warm spots.
10 hrs. Voltage 1.3V.
11 hrs. Voltage 1.8V.
12 hrs. Voltage 2.4V.
14 hrs. Voltage 2.9V
17 hrs. Voltage 3.2V.
18 hrs. Voltage 3.7V. Current stable @ 400mA. Temp slightly above ambient, no hot cells.
19 hrs. Voltage 4.2V. Ever so slightly warm, will watch this closely and maybe reduce reverse charge current.
22 hrs. Voltage 5.5V. Still watching temps, no change from before.
23 hrs. Voltage 6.5V. Confirmed polarity reversal with a DMM.
24 hrs. Voltage 7.5V Temp and current stable.
At the speed of reverse charging now I'll back off the current to 300mA until the morning when I can keep an eye on it every couple of hours.
Then I'll wind it back to 400mA and let it stabilize for a bit before continuing this log.
7am 28 Nov
After overnight reverse charging at the lower 300mA rate the battery was quite cool and @ 9.5V.
33 hrs. Voltage 10.3V. Reverse charge returned to 400mA.
34 hrs. Voltage 10.7V.
35 hrs. Voltage 10.7V. Interesting, have we reached some plateau ?
36 hrs. Voltage 10.7V. Battery still cool to the touch. PM sent to Circlotron for advice and Amps reduced to 100mA while I await his reply. 9.6V (slowly falling) @ 100 mA........7.7V now ~15 minutes later.
37 hrs. Voltage 8.1V @ 100mA with a still reversing charge.
38 hrs. Voltage 8.9V @ 100mA. With reply from Circlotron I'm lifting charge to 200mA (1% of C) to observe battery behavior.....9.4V. Will probably lift current more in another hour or so.
39 hrs. Voltage 10.2V @ 200mA reverse charge. (1% of C)
40 hrs. Voltage 10.3V. Current lifted to 300mA.....10.6V. Battery @ ambient temp.
41 hrs. Voltage 10.7V @ 300mA. Will it go higher or have we reached the 10.7V plateau again ?
42 hrs. Voltage 10.9V @ 300mA.
43 hrs. Voltage 10.9V @ 300mA.
45 hrs. Voltage 10.9V @ 300mA. Battery slightly warm. Will run until the morning, say ~56 hrs then leave to settle and measure OC voltage before deciding if more reverse charging needs be undertaken or to start the discharge prior to forward charging. Much will depend on results from another overnight reverse charge.
48 hrs. Voltage 10.9V @ 300mA. Battery slightly warm. Plan is to do some OC voltage measurements over maybe 30 minutes while the battery stabilizes before draining it prior to the forward charge.
Will also log the discharge which might at the end be able to indicate the success of this attempted recovery...or not. Till the morning....
10am 29 Nov
60 hrs. Voltage 11V @ 300mA. Reverse charge terminated.
Open circuit voltage after 10 mins 8V.
Nearing a stable but 'reversed' voltage 7.5V ~20 mins after reverse charge terminated.
7V and still very slowly falling.
6.75V and nearly stable reverse voltage.
Discharge commenced. 11.35 am
Load: 30W 12V sealed beam spotlight, 2.25A measured draw @ 13.2V.
Actual battery drain 1.3A
+10 mins 1.16A, 3.7V
+15 mins 1.13A, 3.3V
+20 mins 1.1A, 3.15V
+25 mins 1.08A, 3.1V
+30 mins 1.05A, 3V
+35 mins 1.01A, 2.75V Starting to noticeably fall away.
+40 mins 0.95A, 2.4V
+45 mins 0.88A, 2V
+50 mins 0.8A 1.55V
+55 mins 0.74A 1.2V
+60 mins 0.69A 1.0V
+65 mins 0.64A 0.8V
+70 mins 0.6A 0.7V
+75 mins 0.55A 0.55V
+80 mins 0.5A 0.45V
+100 mins 0.25A 0.2V
+110 mins 0.21A 0.15V Battery now resting to observe any recovery....immediately to 1V then to 1.75. Will rest a further 5 mins......2.45V.
Further discharge started.
+15 mins 0.17A 0.125V
+65 mins 0.09A 0.06V
Forward charge commenced. 3pm 29 Nov
Target = ~13.8V with charge current falling indicating battery fully 400mA (2% of C rate) trickle charged.
0 hrs. Voltage 1.3V @ 400mA
+20 mins Voltage 1.5V
+45 mins Voltage 1.8V
1 hr Voltage 2.0V
2 hrs Voltage 2.5V. Battery temp barely above ambient.
2.5 hrs Voltage 3.0V
3 hrs Voltage 3.2V
4 hrs Voltage 3.8V
5 hrs Voltage 5.0V
6 hrs Voltage 6.5V
7 hrs Voltage 8.0V @ 400mA Reduced to 300mA for overnight. Battery cool.
12 hrs Voltage 10.2V @ 300mA
14 hrs Voltage 10.4V @ 300mA
15 hrs Voltage 10.5V
23 hrs Voltage 10.6V @ 300mA. Charge rate increased to 2% of C: 400mA = 10.9V.
26 hrs Voltage 10.8V @ 400mA.
27 hrs Voltage 10.7V. Battery barely warm.
30 hrs Voltage 10.7V
40 hrs Voltage 11.0V @ 400mA
41 hrs Voltage 11.1V
43 hrs Voltage 11.2V
@ nearly 44 hrs....75 min power cut. Measured OC battery voltage 11V. 1 hr later 10.8V.
Forward charge resumed (45 hrs) 1 pm. Voltage 11.0V @ 400mA.
46 hrs Voltage 11.3V
47 hrs Voltage 11.4V
56 hrs Voltage 11.8V. Still @ 400mA and battery still cool.
65 hrs Voltage 12.1V
66 hrs Voltage 12.2V
70 hrs Voltage 12.3V
73 hrs Voltage 12.4V
76 hrs Voltage 12.5V
78 hrs Voltage 12.6V
87 hrs Voltage 13.1V
88 hrs Voltage 13.2V
89 hrs Voltage 13.3V
90 hrs Voltage 13.4V
91 hrs Voltage 13.7V CC'ed voltage rising quite quickly now as we approach the 13.8V PSU setting.
Expecting to see the current (400mA) start decreasing soon after 13.8V battery voltage is reached.
~92 hrs
Midday Dec 2
Target voltage (13.8V) reached with battery draw current quickly reducing .....now 340mA.
93 hrs Voltage 13.8V Current 230mA.
~30 mins later current 180mA.
Will leave charging @ 13.8V CC until no further current decrease is noticeable, then rest battery for an hour or so to get a stable OC voltage before attempting any discharge/capacity tests.
~95 hrs Voltage 13.8V @ 120mA.
From discussion in reply #33 charge voltage has been lifted to 14.5V where current increased to 250mA and falling reasonably quickly. In just a few minutes down to 200mA.
I'm calling recovery forward charge finished at this time as the little further charge can/will be added to the battery. ie. insufficient to make any significant difference to upcoming load/capacity tests.
3.15pm Battery resting.
+5 mins OC 12.75V
+15 mins OC 12.64V
+30 mins OC 12.6V
1hr OC 12.56V
Discharge log 4.50 pm.OC voltage 12.54V
Load: 12V 30W handheld spotlight.
Drawing ~2.2A battery voltage ~12.3V
Attempting a dual measurement histogram with SDM3065X bench DMM........
+30 mins Voltage getting close to 12V and current just over 2A.
+50 mins Voltage 11.9V Current 2.07A
2hrs Voltage 11.78V Current 2.04A
3hrs Voltage 11.6V Current 2.01A
4hrs Voltage 11.38V Current 1.99A
Discharge stopped. Battery recovered to 11.62V
Battery returned to charge, target = 14V @ 1A CC (5% of C)
0hrs Voltage 11.9V @ 1A
9hrs Voltage 14.0V @ 0.1A
Charge stopped.
+2hrs static voltage 12.54V
Initial/preliminary findings/summary.
~40-50% of battery capacity recovered from this method.
Unknowns
Will this battery hold charge for any useful period ?
Will these initial battery test results improve or degrade with further use ?
Further battery conditioning
Maybe some time on the desulphator built many years ago.
TBC..........
Please note: ongoing edits throughout this post for text clarity and better understanding.