Dead batteries - with odd charging circuitry

This is entirely my fault. I bought a mini chainsaw to make a video about, but as I'd featured another variant at that time I held off and ended up storing the unit and its batteries for about three years. When I rediscovered it I found that both batteries were damaged beyond recovery by over-discharge. Usually if the cells have dipped just below about 2.5V they can be gently eased up to 3V and then charged fully. But these ones have suffered long term discharge damage to at least one cell in each pack, causing rogue self discharge.
When a cell does not maintain its voltage after charging (allowing for a slight settling of voltage) then it's time to let it self discharge completely and recycle it. The losing of charge usually indicates a damaged separator between the electrode layers.
Odd circuitry though. They seem to have gone a different charging direction than usual, with the charge MOSFET drive being level shifted to switch a MOSFET on the other supply rail.
I'd guess that the charge MOSFET output is active at all times, except when an end of charge state is detected, by one of the cells in the battery reaching 4.2V.
The moral of this story is to ensure that all power tool batteries are given a top-up charge every so often. Especially the ones that don't get used for long periods of time.
If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:- www.bigclive.com/coffee.htm
This also keeps the channel independent of KZbin's algorithm quirks, allowing it to be a bit more dangerous and naughty.
#ElectronicsCreators

[@graemedavidson499]

It’s always good when a chainsaw does not cost an arm and a leg.

[@Frankhe78]

One of the occupational hazards of being a hoarder, things break whist they are not being used.

[@TopEndSpoonie]

Rather than recycle the whole pack, remove the good cells and reuse them as a USB power pack. They won't get too stressed in this mode of operation and you get to re-use rather than just recycle them all.

[@daifeichu]

When I saw the thumbnail I thought you were going to go full AvE and open the battery with the chainsaw.

[@samakovamk]

That voice needs to be reading the 10pm news, "theres a slight problem in Gaza", "one moment pleaze"....thanks Clive, very informative as normal......best regards

[@zh84]

I submit that lithium cells, for all their power and efficiency, are not the right choice for something that is only used occasionally. Then they are likely to discharge and become unusable. If you are a professional gardener, lithium cells would be suitable for a portable tool you use often, but for an amateur, when the tool may lie unused for months, the power pack is likely to fail unless you leave it plugged in all the time - which is a waste of a socket.

[@josephking6515]

If you stand on the one on the floor Clive, you'll end up with a

[@MavisCruet-w6d]

Am I the only one who was hoping to see Clive run a chainsaw through a battery pack?

[@davidrobertson1980]

Now there's a use for your vape batteries ;) save the day when you can't get a replacement fast enough and are too damned lazy to use a hand saw lol

[@BillyNoMates1974]

ah yes the zombie hand chopper is back

[@MasterBakerVideos]

I bought one of those modules to convert an old Ni-Cad batt pack to Li-Io. Works great at keeping each cell charged - better than the old system, which had no current limit when charging. Every problem batt pack I've opened typically has one bad cell, while the rest are fine. So many good batts end up in the waste bin. If they made it easier to access and replace the cells, there'd be less waste but I'd image manufacturers don't want that.

[@CrazyOregonBeaver]

2AM....

[@amorphuc]

Interesting and thanks Big Clive. I finally broke down and got one of these little saws when it was $30 and I have to say I'm totally impressed. It will chop through a 4" limb easily. I think it must have been a few years ago seeing your video that has kept that on my wish list for such a long time.

[@jacquesmalan3621]

Was waiting for you too pull an AVE. i miss his old bolter stuff

[@DirtyPlumbus]

I recently purchased an American made Hart battery-operated drill and was furious to find the battery was dead and that buying a new one for $60+ was no guarantee.

[@wileymarm0t]

I really appreciate your breakdowns and your painstaking analysis.

[@SeanBZA]

Had that with a replacement laptop pack. First one was 7V8, for a 3 series pack, so was returned and replaced. Second was 9V, but was in undervoltage lock out. So a small bit of work with a 1mm drill bit to get a pair of holes to the end of the pack, and a charge at 1A for a few minutes to raise the voltage up to 11V, and the pack decided it was happy again, and started to charge. After 12 hours it was still at 77% capacity, but fully charged, so it took a few cycles of full to near flat to get the charge controller to agree with the battery, and bring it back up to 100% again.

[@skovgaard79]

Incredible breakdown of battery safety and circuitry! Your explanation on lithium cell maintenance is eye-opening. thanks

[@gregorythomas333]

I have had lithium batteries down extremely low but never saw one actually go negative charge!

[@AndrewFremantle]

I'd be interested in seeing you try your hand at battery-pack rebuilding? Get some new cells and return these packs to operation!