Again this week, we see another example of what kind of damage a defective Lithium Ion battery can do, with the recent Samsung situation. Probably the most difficult thing is not that the batteries fail, it is how they fail–dramatically, with flaming fires and possibly explosion. It makes people wonder if any lithium battery is safe. At times, we think about the same thing.
Most of the lithium technology used in phones is cobalt or manganese-based because of the incredibly high energy density needed for today’s devices. The internal anode and cathode are insulated from each other by a vanishingly-thin separator again, to achieve the highest possible energy density (since a thicker separator detracts from energy density and thus battery life). These devices are highly competitive and every minute of battery life is part of their competitive advantage. Unfortunately, any breach to this very fragile separator creates a short circuit which ignites the flammable electrolyte used in these cells.
Even with this, they are remarkably reliable, and for the hundreds of million batteries that are produced, we hear of perhaps a thousand or less failures per year, in the range of a few failures per million cells produced. This is not meant to minimize the problem–we will never be happy until these failures vanish to zero, if that is possible. If it is not, the next best thing would be for the remaining failures to be non-violent.
When we were doing the research on our Model 1900R3, we looked at a broad array of battery technologies. We were dissatisfied with the long term (5-8 years) performance of the sealed lead acid (SLA) technology we were using. Some customers really like the idea of a battery that can be recharged without removing it from the clock, so we wanted to continue supplying a rechargeable version. Very little new SLA technology is being produced today, and so we see no long term improvement in this technology forthcoming.
Our very first and foremost concern is safety, and energy density less so. After looking at many alternatives, we settled on LiFePO4 because it is inherently much safer than the cobalt and manganese-based lithium ion technologies. We saw tests done on the cell we use, the Headway 38120, in which they were shot with bullets, crossbows, sawed in half, and other un-thinkable things, without any fire or explosion resulting (PLEASE DO NOT TRY THIS!!). The Headway 38120 uses a more robust separator. Their long term performance and life is excellent, indicating that the critical separator holds up very well over a long period of time as does the rest of the internal chemistry. In other words, they appear to be a very stable cell technology.
The way we use these cells in the 1900R3 would never subject them to much electrical stress–better than 10x less than what they are designed to handle. Indeed, this battery cell was designed to be used in much more demanding, rigorous applications than anything our modest little clock application would ever require.
Additionally, the Model 1900R3 is internally protected with double fusing (permanent and resettable fuses) on the battery charge input, the battery itself, and the output terminals to the clock. So it would take a great deal of deliberate effort for any outside electrical event to get to the internal 38120 cell–let alone do it any harm.
Probably the most important thing is to avoid uncharted territory. With lithium ion cells, including the LiFePO4 cell used in the 1900R3, very little information exists on the safety impact of “float” charging. “Float” charging means leaving the battery plugged in for extended periods of time (days or weeks or months) after full charge is reached. We STRONGLY discourage this. It isn’t because there is a known problem; it’s because the impact on the cell technology has not been researched thoroughly enough for anyone to know for sure what will happen. So we recommend disconnecting the charger fairly immediately after charging, and our instructions reflect this as well.
And, of course, it is important to charge above freezing temperatures and use or store below 100 degrees fahrenheit.
We feel the Model 1900R3 is one of the safer lithium batteries available. We have been using 1900R3 batteries to power our clocks for well over 5 years now, with excellent performance in every measurable way, and little to no degradation in performance. But, no one can 100% predict long term safety with any battery solution. Therefore, the final decision is yours as the customer. If you still feel unsafe with Li Ion technology powering your clock, we suggest you select one of our other battery solutions, all of which are renewable, using traditional alkaline D batteries and advanced electronics to stabilize the output voltage and provide your clock with the best power source available today.
If all of this recent news disturbs you, and you presently own a 1900R3, we would be happy to exchange it for another battery solution.