Battery or electronics advice needed

drew1 · 08-24-2020, 07:48 AM

I have a problem with Lowes Kobalt 40 V 2.5 Ah Lithium Ion battery.

- In chainsaw and weedeater on for a couple of seconds and off. Same thing when trigger is mashed again. After sitting for various amounts of time same problem, no continous run. Another battery runs both tools.

- 2 bars out of 4 on charge indicator, but when battery recharged to 4 bars, same thing. Voltage checks over 37 Volts accross terminals..

- From Kobalt 40V Saw manual:
This Lithium-ion battery is equipped with an internal circuit breaker which will automatically shut off the power to the tool and then reset itself once cooled. Follow these steps if an overload occurs while under heavy use:1. Release the power switch and restart tool by depressing switch. 2. The battery may need to be removed for approximately 1 minute, allowed to cool and then reinstalled for use.

-From the picture below it is seen there is no leakage from the battery's cells or any discoloration from heat. No bug nests or egg pouches either.

- The arrow on the second picture shows what I think is the thermal autoresetable breaker. Not visable is the printing of 40, in my mind meaning 40 C or a little over 100 F. Also the leads have 1/4 " holes for screw mounting even though soldered here?

Can anybody help identifyy this part. I have seen no OL on magnetic starters that look like this and an electrical supply place has seen nothing like this.

asphaltgambler · 08-24-2020, 10:39 AM

I think its likely that the battery pack has seen too many cycles. It show voltage but what happens under load?

aschen · 08-24-2020, 01:27 PM

That may be the current sensing resistor? The thermal fuses and temp monitoring are usually glued to the cells I believe.

If you have access to terminals of each cell maybe you can locate a bad one.

john70t · 08-24-2020, 01:30 PM

Load testing each cell dynamically would probably give best .

Measuring Voltage after recharge and after use will give an indication of which is bad.

If it's possible to use it with the cover off...there are cell phone simulators which might identify the bad cell/s.
https://prepperswill.com/do-thermal-imaging-app-work/

https://www.bing.com/videos/search?q=Kobalt+40+V+2.5+Ah+Lithium+Ion+battery+ce lls&docid=608022482793334397&mid=996765A2391174D384A5996765A2391174D384A5&view=detail&FORM=VIRE
There might not be individual new cells available, but the tested-good ones could be kept for future problems.

Cajundaddy · Cajundaddy's Garage

No mention of battery age or # of cycles but my guess is 1 bad cell. You might be able to repair it if you have a good meter and know what to look for. If it is over 5 years, simply replace it.

drew1 · 08-24-2020, 07:05 PM

Thank you for responses. It is about 3 years old. Replacing may be the best way, but you know about what they say about "fools rushing in", the battery is about $80, and I figured this old man might learn something. I charged it last spring when I had the problem and it was charged up to 4 bar or full capacity. It is now half capacity but a little over 37 Volts. I'm guessing it was very little more at full charge since 5 cells X 7.2 Volts = 36 Volts. Checking was done with a Fluke DVM that was calibrated while I was still working. If it had measured 34 Volts or so, I would have thought a weak cell and disposed of the battery.

I have not load tested. I have a good battery. Newark and Mouser have reasonable priced high watt resistors that I could put inline between the battery and probably my little weedeater to get voltage drop and figure out the current. Jumping whatever this component is I could compare the bad battery to the good and check the cells with an infared thermometer to find out if one is a lot different.

Thank you to everybody for sharing your knowledge.

drew1 · 08-26-2020, 10:18 AM

Right now I am doing nothing since I have one good battery. It would be worth $40 I think to repair, but I cannot find the part that I think is defective and have no more cells if one or two are bad. With shipping it would cost me $32 to get the two resistors I think I need and a terminal block to test which would be stupid if I cannot fix it.

I will note that a reconditoned battery can be ordered from Lowes for $50, but it has twice as many bad reviews as good and some of the questions deal with the same problem that I am having.

I at the stage of throwing away junk so my kids will not have to in a few years, but may save this battery for cell harvesting when the other one goes.

Bigtoe32067 · Bigtoe32067's Garage

Throw it away and buy the new one. The reconditioned ones suck.
Good luck
Tony