This is for new owners, or people thinking of getting one. PeakOilGarage started a list of things for you to do; this is more a list of things to expect. Please pile on with things I forgot, or haven't run in to yet. This is what will be different after you get an a123Systems (Hymotion) L5 battery installed in your â€™04-or-later Prius. It may sound like a negative list, but Iâ€™m actually pretty happy with the pack. Itâ€™s just that itâ€™s a big purchase, and people are more likely to take the plunge (and be satisfied with what they got) if they know what to expect--and there are some tradeoffs. Here we go: 1. Your wallet is $10,400 lighter. 2. Your load capacity is 200 pounds less. I mean, your carâ€™s load capacity is less. Maybe yours is too while you contemplate the financial damage. 3. You can no longer use the storage compartment under the cargo area. 4. Your spare tire is removed from the storage well. This is actually the thing that bothers me the most. Options: a. Put the jack & tools next to the new battery, and strap the spare tire in the cargo area (Toyota provided straps for this purpose, because the full-size tires donâ€™t fit in the well). Lose some cargo room. Note that thereâ€™s no protective bag or anything that comes with the kit. b. Carry flat juice and a patch kit. Lose the ability to keep going if a tire blows. (I have to admit that doesn't happen often). c. Upgrade to 16â€ run-flat tires and wheels. Lose a lot of money and some of the mpg you just bought (theyâ€™re heavier, and in the worst place for more weight). 5. You have to plug in your car now--there will be a hole drilled in the left side of your rear bumper. Itâ€™s easy enough to do, but you should do it every chance you get. The brake lights will come on to show when it is charging. You need a 25â€™ 14awg cable or a 50â€™ 12awg; you donâ€™t get one with the pack. Shorter cables and smaller awg ratings are fine too. 6. The car will occasionally (maybe once every 30 miles?) go â€œbeep-beep-beepâ€. Thatâ€™s the pack and the car arguing about what mode the car should be in. Just ignore it. 7. The pack will repeatedly ask the multi-function display to display the pack charge status. Which is great, except it also tries to display the standard battery status, and then gets overridden, causing flicker. You get used to that fast enough. It will also sometimes switch to the charge status screen while youâ€™re trying to use another screen, which is more annoying. Thatâ€™s pretty much it. You can drive the car exactly as before, and while the pack is charged, youâ€™ll probably get somewhere around 100mpg. Of course, at that mpg range, little things can make a big difference. Accelerate slowly, donâ€™t use climate control, avoid hills, avoid short cold trips (or install a block heater), etc. Also note that when the pack loses its charge (they say 30-40 miles, weâ€™ve been seeing just around 40â€”note that the pack Toyota is testing supposedly only works for 6 miles) it goes back to the normal 50mpg. If you go 40 miles at 100mpg and another 40 miles at 50mpg, your average is only 67mpg, which can be disappointing. Charge the pack every chance you getâ€”carry a cable in the car. There is an on-off switch for the pack on your dash. You probably just want to leave it on all the time, although itâ€™s nice to be able to turn it off if Toyota service is picky, or you are troubleshooting, or you are on a long trip and think the charge will make a bigger difference later (but donâ€™t turn it off while youâ€™re driving!). Thereâ€™s an LED to show that the pack is charged and ready. If it ever flashes, count the flashes. Stop the car for a few minutes, drive again, and see if it flashes again. If so, call your installer.