First the thieves came for the car radios, and I did not speak out. Then it was airbags. And now, according to Toyota dealers, battery packs are increasingly becoming the target of smash-and-grab thieves.

The Toyota Prius, as you may know, is a hybrid—it has a small 1.5- or 1.8-litre engine, along with an electric motor that's driven by a battery pack (nickel-metal-hydride, NiMH, in the case of normal Priuses, and lithium-ion for the plug-in hybrid version). Like most batteries, the one in the Prius gradually loses its efficiency over time, eventually necessitating a replacement.

The cost for replacing a Prius battery pack is not insignificant—outside of the warranty period, it's about $2,500 in the US. Curiously, it's much cheaper in the UK: just £800 according to Toyota.

The second-gen Prius, released between 2003 and 2009, was a huge sales hit—and now, many of those vehicles are coming up to the point where they need a new battery. Some third-gen Priuses, which went on sale in 2009, may start seeing battery fade as well. That demand for replacement batteries, it would seem, is fuelling a number of battery thefts in California.

KGO-TV is reporting that there has been a "rash of thefts in San Francisco," and quotes a Toyota dealership that has replaced "quite a few" stolen batteries. Car thieves smash the rear windows of the Prius, cut through the connecting wires, and then pull out the 150-pound (68kg) battery pack. KGO reports that the thefts are being carried out in about 20 minutes.

According to John Nashed, who had his Prius broken into, "We looked on Craigslist, the batteries are going around $900 to a $1,000"—a lot of money for a 20-minute smash-and-grab job, and, for a prospective buyer, a good discount over an official replacement battery. Prius owners should of course be very wary of buying a used battery from the black or grey market; you have no idea how many miles have been driven on the battery.

Yahoo Auto reports that the thefts seem to be localised to San Francisco at the moment, and also that Prius battery packs aren't marked with a serial number or VIN, which makes them easy to sell. Apparently, according to Luscious Garage in San Fransisco, if you're a Prius owner who wants to mitigate against theft, you should replace the battery's existing 12mm bolts with tamper-proof bolts. Presumably that won't stop the thieves from first smashing your windows and damaging your upholstery, only to find out the battery can't be removed, however.

As electric vehicles become more popular, batteries will increasingly become the target of theft. The good news is that it should be fairly easy for car makers to secure the battery pack to the chassis in some way; and of course, the sheer size and weight of some battery packs should deter petty car thieves. The Tesla Model S battery, for example, comes in at around 1,000 pounds (450kg).