Photo: Jim Merithew/Wired.com 
Tesla Motors is downplaying a claim that completely draining the battery in its electric sports car “bricks” the vehicle, a problem that could in theory apply to any electric vehicle and is best avoided by simply plugging the car in regularly.
In what is sure to become another rallying cry for critics of electric vehicles, a report published by Michael Degusta of The Understatement claims fully discharging the Roadster’s massive 53 kilowatt-hour lithium-ion pack effectively kills the battery, rendering the car inoperable. This, he claims, can happen even if the car isn’t being driven.
“A Tesla Roadster that is simply parked without being plugged in will eventually become a ‘brick,’” Degusta, who has placed a $5,000 deposit for Tesla’s forthcoming Model X crossover, writes. “The parasitic load from the car’s always-on subsystems continually drains the battery and if the battery’s charge is ever totally depleted, it is essentially destroyed.”
Degusta says he interviewed an unnamed Tesla regional service manager who identified five unnamed Roadster owners who have experienced the problem in a variety of circumstances, including using a 100-foot extension cord to charge a Roadster. He argues, without offering any proof, that the forthcoming Model S sedan could experience the same problem.
Tesla Motors downplayed Degusta’s report, arguing the issue he raises isn’t a technical problem so much as an issue of properly maintaining the vehicle. The company likens the need to maintain a minimal charge to ensuring there is sufficient oil in a conventional engine.
Photo: Jim Merithew/Wired.com
“All automobiles require some level of owner care,” the company said in a statement. “For example, combustion vehicles require regular oil changes or the engine will be destroyed. Electric vehicles should be plugged in and charging when not in use for maximum performance. All batteries are subject to damage if the charge is kept at zero for long periods of time.”
The issue comes at a critical time for Tesla Motors and for electric vehicles. Tesla is preparing to ramp up production of the Model S sedan and recently announced plans to launch the Model X in 2014. More broadly, electric vehicles from Ford and others will follow the Nissan Leaf and Mitsubishi i to market.
Tesla Motors spokesman Ricardo Reyes would not comment beyond the statement, but Tesla’s main point was echoed by EV advocates and Thilo Koslowski, an auto analyst with Gartner.
“This isn’t all that surprising,” Koslowski said. “This is what you’d expect with batteries. The same thing will happen with the battery used by your internal combustion engine. If you don’t maintain it, it will go dead. The issue here for Tesla is the battery is of course a significant part of the drivetrain. It is very expensive, and there are liability issues.”
Degusta said in his post that the only solution to the problem is replacing the pack, which can cost more than $30,000. Koslowski said it is possible to revive a “dead” battery. However, it is a complicated, time consuming process and there’s a risk the battery was damaged by being depleted. This makes it unlikely an automaker would be willing to revive a dead pack.
Tesla argues the problem is not so great at Degusta alleges because the Roadster warns owners as the state of charge approaches critical levels, providing ample notice of the need to plug in. It also notes the risk of the battery depleting over time is an issue only if the car is left idle for extended periods. Most of the 2,200 Roadsters on the road will alert the driver — and Tesla Motors, if the owner has opted into the program — when the state of charge is critically low.
“Tesla batteries can remain unplugged for weeks (even months), without reaching zero state of charge,” the company said. “All Tesla vehicles emit various visual and audible warnings if the battery pack falls below 5 percent SOC [state of charge].”
This could, in theory, be an issue for any electric vehicle, but it is one General Motors and Nissan said they’ve considered in the design of the packs in their cars with cords. Although the Chevrolet Volt plug-in hybrid features a 16 kilowatt-hour pack, only 10.4 kilowatt-hours is used to actually propel the car. The rest is a “buffer” designed to prevent over-charging or depleting the pack, said company spokesman Robert Peterson.
The Nissan Leaf features several visual and audible warnings to alert drivers to the declining state of charge, and the pack was designed so it cannot be fully discharged, company spokeswoman Katherine Zachary said in a statement.
“One element of the battery management system is a failsafe wall that stops the battery from reaching zero state of charge, even after a period of unplugged storage,” she said.
Koslowski and others said the simplest solution for any EV owner is to plug the car in whenever possible, particularly if it’s going to be sitting for an extended period. This is akin to putting a trickle charger on the battery under your hood.
Indeed, this is just what the owners’ manuals for these cars suggests. Tesla, for example, warns that “over-discharge can permanently damage the battery” and “if storing for more than 15 days, it is strongly recommended that you keep it plugged in.” The Tesla manual warns that a fully charged Roadster pack will drop as much as 50 percent in the first week, then lose about 5 percent per week thereafter. Tesla says a fully charged battery would require about 11 weeks to fully discharge if the vehicle were not used.
Tesla warns its customers of this fact and, according to Green Car Reports, has buyers sign a document acknowledging their responsibility to maintain a charge in the pack and stating that any damage caused by failing to do so is not covered by the warranty.
At the bottom line, electric vehicles are a fundamentally new technology for most consumers, one with different maintenance needs. As more automakers follow Tesla, Nissan and General Motors to market, the entire industry will have to do a better job educating prospective EV owners about the maintenance requirements of cars with cords.
“There will be some maintenance requirements that will go away when you transition away from internal combustion engines, but there will be some new ones that people need to be aware of,” Koslowski said. “The industry has not done a good job explaining this, and outlining the long-term maintenance requirements.”
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