Lithium battery pack behavior...

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Greetings.
A power tool uses its own brand name battery pack with five 18650 cells. Runs well. Lasts very little, like 1 minute and it is supposed to last ~20 minutes.
Charger used is the same brand intended for such battery packs, was supplied original with the tool. Gets full charge signaling light in about 5 minutes; It took like a couple of hours when everything was new.
Tried a second battery charger, same behavior reaching full charge in just 5 minutes, lasts about 1 minute operating the tool.
Batteries are less than 50 cycles of charge/discharge in very normal use, never abused.

What would be your opinion diagnosis ? How can the health of the (5) packs be determined with no doubts ? Can their internal charge/discharge management be failed ? Can both chargers be failing somehow ? Can the tool be signaling to the packs to stop operating the cycle / delivering the energy ?

Many places on the web with details on charging but not much on diagnostics and failure modes, life expectancy.


-Image borrowed from web-
 

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Just a guess without seeing it... one of the batteries has died. To some degree the others will take up the extra charge but the bad one will result in overall lower output voltage when under load and it will limit the current available. It isn't unknown for recycled batteries to be used in new equipment!

Brian.
 
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One or more cells has developed high internal resistance. Charging current and Ohm's law cause it to develop excessive voltage. It fools the charger into thinking the battery pack is full.

Another thing that happens... it gets overly warm during charging. If a temperature sensor is present then it causes charging to shut off prematurely.

The cell hampers the pack's overall performance.

There's also the possibility the motor developed a need for extreme current, with the result that it rapidly drains the battery pack. You can test for this by hooking up a substitute power supply.

To locate the faulty cell you need to unwrap the pack. You may need to cut tape with a knife. Be careful not to slice into a cell or temperature sensor. Expose cell terminals so you can measure each with a voltmeter.

Measure each cell while charging. Measure each cell while running the appliance. One or more cells is going bad.
 

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Thanks, gentlemen.
Pack #1 tested with each of the 5 cells at 4.15 to 4.17V after overnight from being charged.

Bench running the tool with cells exposed, not a spec of dust nor corrosion, look new inside. Not cutting grass load, tool runs with none of the cells under 3.7 to 3.9 V. Continuing to test run, all equally lightly warm to touch -guessing 45C- and tool stops at 14.5 V of the 20V nominal pack.

In a couple of minutes off, cells 'self-recover' from equally ~3V each rising yielding ~19.5V for the pack, and tool starts fine again but stops in about another minute running, at the 14.5V pack level. At no moment, running or stopped, any of the cells shows significant less voltage than others.

Ordered only one of these to see how much chinese lie (10 years warranty) yes, sure. Warranted if not being used, in storage... maybe



So far seems no single cell failure, no gross thermal protection, as the tool can restart immediately in few seconds after self-stops.
 

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Hi Mr Brian, I tried to send you a PM, but it's not available.

I need you to check my post please:
https://www.edaboard.com/threads/de...d-even-taking-all-mosfets-out-the-pcb.406414/
 

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It is recommended that you purchase branded batteries and make your own battery pack for welding machines, which will be more secure. Online purchases that are not made on well-known online shopping platforms are usually not guaranteed. For example, batteries may be recycled or faulty, or they may be storage batteries (storage capacity is guaranteed but discharge rate is not enough). Take a look at online shopping platforms https://www.jd.com Or www.taobao.com
--- Updated ---

Sorry, www.taobao.com is incorrect. Look at this https://www.tmall.com
 

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To determine the health of the battery packs with no doubts, you can use a multimeter to measure the voltage of each of the 18650 cells in each pack. A healthy cell should have a voltage of around 3.7-4.2 volts. If any of the cells are significantly lower than this or are showing signs of swelling or damage, then it's likely that the entire pack needs to be replaced.
 

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The new battery pack from post #3 arrived; it does last like 20 minutes running normal, takes about 1 hour to recharge. So the problem is not any charger nor the tool. Original battery packs failed waaaay before a reasonable number of duty cycles. Viva China !
 

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No information along the whole thread about current drawn from the battery. May be just normal operation.
 

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