Warning - Changing Battery
Technologies Can Be Dangerous 

By Ted Twietmeyer

It came to my attention recently that battery manufacturers are selling identical form and fit replacement batteries with different technologies (or chemistry.) These replacements allow "upgrades" from lower capacity nickel cadmium to other technologies. It is hazardous and potentially lethal to change a battery in any appliance or electronic device to a different battery technology. The following is a copy of a message about this I sent to Ebay on this matter:

"I'm am electrical engineer, and noticed a serious problem while looking for a new battery for our Roomba robot. As you probably know, Nickel Metal Hydride (Ni-MH,) Li-ion and Ni-Cad batteries are all VERY different - both in the chemistry they use and the method they are charged. Past defective Ni-MH batteries have already started fires in cell phones and laptops, causing recalls numbering in the hundreds of thousands. Even Dell computer was bitten by this problem when they were faced defective Sony laptop batteries which could catch fire - with the computer sitting on your lap.

Charging currents, voltages and charging current control protocols are different for each battery technology. When we upgraded our 610 Roomba to use a NiMH battery from the manufacturer, the company (iRobot) sent us a software upgrade "pod" to plug into a port on the robot. Software auto- downloaded itself from the pod into the robot's program memory changed the charging algorithm, charging current, charging time, etc... so the machine can safely use the higher capacity Ni-MH battery.

Most people are totally unware that temperature sensing is a required part of charging lithium technology batteries. Without temperature sensing cells can overheat and become damaged or catch fire. This is why a cell phone taken from a hot car in summer may refuse to charge, until you bring it indoors and let it cool down. Then it will charge.

Ni-MH and Li-ion batteries can catch fire or explode if improperly charged. At the very least battery life and performance will be greatly shortened. I suggest that to limit everyone's liability (like a fire in a home or apartment burning down due to incorrect charging currents) that you institute a policy to make sellers of rechargeable batteries inform all their bidders about the hazards of replacing one battery technology with different one. Currently this isn't happening, creating a serious liability and even a potential for a fatality."

Battery technology is NOT like connecting USB or cell phone cables. Just because a different battery type fits into the battery compartment and the connector plugs in without a problem, NEVER assume it will be safe to use. If you have already substituted a battery with a different technology battery without the manufacturer giving their blessing to do so, remove it now before something bad happens to you, your family or your home.


Never assume that just because nothing has happened yet that you are safe. The federal crash test people thought this, too. They unwittingly proved the volatility of lithium battery technology we all rely on. This happened when several electric cars caught fire more than a day after sitting shut down in a federal crash test storage yard after undergoing crash testing. Super-hot lithium fires of more than 2,000F ignited non-electric nearby test vehicles. No one could have stopped these fires from happening - it wasn't the vehicle cabling to the battery that shorted out. These fires were result of a short circuit INSIDE one of the hundreds of battery cells all electric vehicles have. No one could have ever known which cell would short out after the crash test. Fires have also happened after MINOR traffic crashes, too. Lithium fire hazard isn't limited to total-loss type crashes.

At normal gas or diesel engine vehicle crash scenes, fire departments simply cut car battery cables to prevent electrical fires. In an electric car, you can cut ALL the cables and wires and still have an unpredictable electrical fire break out burning at 2,000F. If you have a electric car and are involved in a crash, even a minor one where no one was hurt, remove ALL your valuables immediately from the vehicle right at the crash scene, then have a friend or relative come get you and your possessions. Don't wait until later to do this - you will never know whether the vehicle might burn to the ground unexpectedly. Even a small fire burning at 2,000F is so hot you can't get near it.

Spontaneous fires within some lithium batteries are the end result of dendrite growth which can start under certain conditions. (Manufacturers may claim this problem has been eliminated but delayed fires may show it is not.) Tiny needle sharp metal crystals known as dendrites can puncture the thin insulation layer between the metal foils and short out the cell. The first dendrite to puncture the insulating layer quickly becomes hot enough to burn a large hole in the insulating layer, causing more shorts to occur, creating more and more heat. This chain reaction can cause a cell to explode from a sudden pressure increase or even catch fire. Then other cells near it can catch on fire. And if you're not home...there goes your house or apartment and maybe even your pets. It makes little difference whether it's a small appliance like a robot with a few cells, or an electric vehicle with hundreds of cells.

Never substitute one battery technology for another unless the manufacturer can guarantee you the charging circuitry can handle a specific different battery technology. An upgrade isn't worth the risk without it. If a fire occurs as a result of a  battery technology change, your insurance company may not pay you for damages for being stupid. At the very least you might get your policy cancelled for proving you're a bad risk.

After properly converting a machine or appliance to a different battery technology, put a label inside the machine's battery compartment indicating it has been upgraded to the new battery type.

Ted Twietmeyer



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