Dead Battery

Last night as I was leaving work I wasn't able to start the Escape. It unlocked and headlights came on, but when I put the key in everything went dark and it started making a chattering clicking sound from behind the dash gauges. The airbag lights were flickering so I figured either something electrical got fouled up and it thought it had been in a crash, or the 12V battery was dead. Fortunately it was the battery. I checked it with a multimeter from the lab and it was fluctuating around 5.5V. This is really low!

Jump starting the hybrid Escape is actually really easy; you don't have to sit there charging the battery with the other vehicle, since the 12V battery isn't actively used to start the engine as it is in a conventional vehicle. Mainly the 12V battery is used to close the relays which connect the high voltage battery to the motor, allowing it to start the engine. It is also used to pressurize the brakes, which is the noise you hear every time you start the car. Once the engine is running it can provide 14V power to charge the low voltage battery and run all the accessories.

When I got home the battery was still dead, which surprised me after 20mi/30min of driving. I popped the caps on the battery and checked the water level and it was WAY down, so I filled it with our reverse osmosis water and hooked up a 1A trickle charger overnight. In the morning it started fine and measured 12.5V. I'll be keeping the jumper cables in the car, but given the relatively light usage this battery gets (no hard cranking as in a regular car) I expect I'll get it to last a good bit longer. It's the original battery with probably 3 years on it, 56k miles.