Here’s a gadget that looks like it could be useful, but I can’t decide. It’s a standby mobile phone battery charger for when you don’t have your charger with you, or access to an electrical outlet. It’s cheaper than a second battery, and because it comes with 5 different adaptors you can use it for other phones too.

It covers a wide range of mobiles but not the Nokia 6000 range interestingly enough, maybe because the voltage rating is too high.

The backup charger costs $30, uses four AAA-type batteries and comes with a handy key ring. The problem is; I’m not sure if it’s a good idea to use a battery to charge another battery. There’s something in the back of my mind about a physics lesson on power dissipation when connecting two similar batteries – I’m sure it’s very inefficient because both will get hot.

Mr Haynes, if you’re reading this, I’m sorry I didn’t pay closer attention in my physics lessons, and can you remind me about matching internal resistances in accumulators?

But in any case, in an emergency maybe it will give your cell phone enough juice to make that mega-important call from the airport when you’ve left your charger in your luggage!

I’m thinking seriously about buying one though. Has anyone ever tried a gadget like this?

Emergency mobile phone charger.