Tool Battery Repair

[Nick Jan]

Yes, one of the repairs in this book does involve hooking up "good" batteries in a series creating a high voltage to burst the "crystals" or "hairs" in the cells. It seems like this could be dangerous if not done properly.

I don't know exaxtly what causes these hairs. I've read it can be caused by overcharging, or running the battery completely dead while under a load, like when you need to cut 3 more inches of the board, and the saw stops, and starts, until it won't go anymore.

[Ed Gerken]

Hello to the group!

My first post here after lurking a few days. Electronics is my first love but I'm also a photographer, a woodworker, metal detectorist and radio nut. I have used "dischargeable" batteries in all these activities. Wherever I can, actually! I'm still no expert, but I've read a lot and tried some of the tricks. I've never seen the info this guy is selling, so I wouldn't know if I'm spilling any beans or not!

A lot of the problems do arise from misuse or abuse. Too much heat or excessive charging current causes the cell to vent, drying it out. So, the best advice is to let the battery cool before charging. Keep tools and batteries in shade if possible.

If the battery heats too much on the charger, give it a break or charge at a lower rate (hard to do with only the factory charger unless you modify it). I think that 1/10th rate is safest, but very slow at 10 hours on the charger. Some cells are better able to handle a higher temperature and charge rate. Otherwise, expect shorter useful life, it's just the name of the game.

Simple chargers just run full bore till you unplug them or remove the battery. An AC timer will let you control things. I keep a record of a pack's fully charged voltage. Use this to guesstimate charging times. Overcharging actually lowers this value, so it's fairly easy to find by experimentation. You'll also spot a pack going bad sooner and can take certain steps to combat it.

Overuse and undercharging are both bad. Rushing the charge process to complete a job costs in decreased battery life. If you count on having batteries throughout a long day, it may be wiser to invest in additional packs and chargers.

Instruct the crew to let packs cool awhile and use them in order whenever possible. If not, suggest maybe they'd like to own the batteries themselves, I bet then they'd take care of them!

What happens is a hot, recently-drained pack is thrust in the charger, then put right back to work while still hot. If it wasn't fully charged, one or more individual cells may be at different voltages and capacities. As a single cell within the pack is nearing discharge, but its neighbors are still well-charged, that weak cell will be charged in reverse. If this continues, it will be severely damaged or destroyed.

Now, this pack with one or more damaged cells will begin to read incrementally lower when charged, and you may notice one or more "hot spots" on the case. These hot cells are now shorted, so they only heat up like a resistor. A cheap digital meter will allow you to test individual cells to detect these faults.

I suppose this is how the little shorting crystals are created. Or perhaps they may just form on their own. Google "silver migration disease," which affects some old radios' trimmer and tuning capacitors.

A simple circuit can be built to charge a large capacitor to "zap" dead cells. Most people that try this just use a 12v battery across individual cells. Preferably not the entire pack at once, but I have read this worked for some. I used a 6-amp car battery charger, popping each cell a few times while monitoring the voltage. Then I charged them as individual cells and reassembled a pack with the rejuvenated ones.

Other failures can be traced to a weak connection or a fusible link. A relatively easy homebrew fix.

Be aware too much heat while zapping or soldering can be dangerous. If a cell vents explosively, I don't wanna hear about it! Also, charged capacitors can be lethal. Even a 12v car battery has electrocuted people. Use common sense and do your testing in small doses.

I didn't have a lot of luck with rejuvenating entire packs, but I did manage to return some of their usefullness. Even if a ruined battery pack couldn't be saved, I did recover a handful of individual cells that I'm using to run an old transistor radio and a flashlight. Out of three packs, only two cells were so badly shorted that I couldn't raise them off zero. But none of the packs are "like new."

There's sources for surplus cells to rebuild your own. About $4 per soldertab C-size or sub-C seems to be the norm, but there are some deals on occasion. I'm going to try subbing high-capacity AA NiMH soldertabs for the C cells in one of my packs. They can be bought very cheaply. Should be a lot lighter, yet run longer!

Model airplane enthusiasts use a lot of LiOn batteries. A warning here is it takes special chargers specifically designed for the battery you are using. A bigger danger seems to be these batteries are not safe if dropped or shorted. They can burst into flames, sometimes many minutes after the impact shock occured. Several people crashed their planes, placed the wreckage in their vehicles only to see it all go up in flames later, while their attention was elsewhere.

Granted the packaging on model plane battery packs is no more than some foil and tape wraps. I recall some laptop computers having similar problems, and more recently, I-pods, cell phones and other handheld devices. LiOn is pretty new to power tools, so I'd treat these batteries with utmost respect at least until some user reports are circulating.

-Ed (promising more brevity in future posts! )