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CORE electric weed whacker woes… HELP!

 
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Location: Western Canadian mtn valley, zone 6b, 750mm (30") precip
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I’ve got friends in three different households who bought Core CGT400 battery-powered weed whackers from a local dealer.  These were all the same model, known as the CGTSD Gasless Powered Trimmer and of course it came supplied with a “Power Cell” (lithium battery) and a charger.

The machines worked impressively well (I even had occasion to use one of them once, for 90 minutes or so).  But, two households have had battery problems — one got a replacement a year or so into the warranty, but one was beyond warranty. The local dealer has gone out of business, so now all three households are glum and nervous.  Amazon advertises the price of replacement CORE batteries at well over $200 before tax & shipping.

I’ve got Makita, Husqvarna, and Ryobi cordless equipment and have never bought any of the CORE machinery myself.  On behalf of my friends, I’m asking if anyone’s got insights on this?  Source(s) for the battery?  Is the CORE company simply bad news and hopeless?
 
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The Li-Ion cells inside are standardized. If you open the battery pack they can be replaced (with some skill). From my experience the batteries tend to go out of balance which damages the one with the least charge in it.

It looks like it has 5 cells with 6.5Ah each in it. Given that they no longer work, at least one cell will be damaged. It might be possible to replace only one cell, but replacing all 6 might be more reliable (The still working cells can be used for other things, like lamps). To prevent this from happening again you will need a battery balancer (equalizes the voltages at the end of charging) or a battery management board (cuts off when the voltage of any cell gets too low). A quick check on ebay gives be 60€ for 10x 18650 3Ah cells. (Which is how many you would need to replace all).
For the same price I can get 6x 10Ah LiFePo4 cells which are a bit heavier and bigger (for the same energy content), but safer and last longer.

If I had to repair such a device, I would remove the battery pack and build one from 6x 10Ah LiFePo4 cells instead.

EDIT: I completely forgot the important part:
A Lithium Battery pack needs a balancer and in your case also a protection circuit that cuts the power off if any cell gets discharged too much.
 
Joel Bercardin
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Sebastian Köln wrote:EDIT: I completely forgot the important part:
A Lithium Battery pack needs a balancer and in your case also a protection circuit that cuts the power off if any cell gets discharged too much.


Sebastian, thanks — you've provided much useful info and I hope Permies members will read it and maybe follow it up, if it is apt for them.  But unfortunately it's not 'in my case' since the machines belong to members of three households, none of which is my household.  I believe none of these people would want to go into the innards of their power cells.  They all seem to be at the point where they will buy another battery pack, or wish to know where they can by one affordably if they need it.
 
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