I got out the booster battery for this purpose. The last time I tried to use it, it did not work, but that was because I'd neglected to read the instructions that say "recharge monthly." Since then, I've set a recurring reminder to do the recharge job. I plugged the booster into the AC adapter, pushed the buttons, waited ten minutes, and when the box said OK, I gave it a whirl.
With a bit of a struggle, the engine turned over and started. Whew!
The booster is now sitting on my desk at the office recharging again. Thanks to Cheryl who gave it to me as a present a few years ago after I had two left-the-lights-on events in two months.