The key to a constantly-charged cell phone

Charge-Key emergency cell phone charger
$17.99 for Apple iPhones or Android phones at Amazon.com

There’s nothing mobile about a mobile phone when you have to plug into a wall outlet for a quick charge. Which is why people have come up with ways to use standard disposable batteries as cell phone boosters. Here’s a particularly cool example.

As its name implies, the Charge-Key fits on your keyring; the Android version actually looks like a traditional key, in black plastic instead of brass. Remove its plastic tip, and there’s a plug that fits either the Micro USB connector on Android devices, or the 30-pin jack found on older iPhones--a version for the new iPhone 5 Lightning connector is under development.

On its side, the Charge-Key sports a plug for connecting a standard nine-volt battery, which is included. Snap in the battery, plug the key into the phone, and a tiny green light tells you that the charging process has begun. You can use the phone while it’s happening, or just leave it alone. I found that one nine-volter would add about 18 percent more life to my phone battery, enough for a decent number of calls. And since you can buy fresh nine-volts almost anywhere, you can give your phone a jolt no matter where you are.

Designed in Billerica, Charge-Key is a fine phone accessory--compact, simple and smart.