New mobile phone battery missing

Before 7pm I decided to check my mobile phone for the current time, and realised it wouldn't turn on. I thought it odd as I had only recharged the battery the day before and hadn't used it except to check the time. So I took it out into the lounge room and plugged it into the power point socket. Then around 7:10pm I went out (on foot) to do some shopping and got home around an hour later. After tea was finished I decided to check on the battery status of the mobile phone and the stupid thing still wouldn't turn on. By rights it should have been fully charged.

This mobile phone was my brother's which he lent/gave to me. The backing has never been taken off since I've had it and frankly, I didn't know how to take the backing off until a little while ago. I rang my brother asking him to come over to take the backing off for me, as I had thought the battery was completely lifeless. This mobile phone has been dropped and has had water damage and wasn't that very good for taking videos but the picture function was great.

When my brother took off the backing he said that "It doesn't help if it doesn't have a battery in it." Sure enough as I looked there was no battery in the mobile phone. Where the bloody hell did the battery disappear to? "@@@# @%$# AND ADD MORE SWEAR WORDS HERE!" It was working fine the last time I checked it today which meant it had a battery in it then.

I must admit I had a very strange feeling something was wrong when the mobile phone wouldn't turn on after I tried to recharge it. But I did not suspect the battery to be completely missing altogether until I saw it. So it seems that whomever is doing this is a kleptomaniac.

LIST OF MISSING MOBILE PHONE RELATED ITEMS:
1. My entire previous mobile phone
2. The battery from my current mobile phone
3. And, the CD software (computer software) that came with the current mobile phone.

I have also previously had a 4GB memory stick go missing within the last 5 months that I'm only just mentioning now.

At this point in time I cannot add any photos of my current mobile phone. I'll add photos as soon as I can. However, my dear brother has lent me his newest mobile phone -a Grape coloured "Telstra Smart-Touch". It's an Android of some sort. Shit, if that goes missing I'll have to buy my brother a new mobile phone?

My current question is did whomever take my mobile phone battery take it because they needed to replace the battery in the mobile phone they previously took? If so why didn't they just recharge the battery the same way I had to do it? Why did the computer CD software also get taken for my existing mobile phone when that mobile phone was not taken just the battery was?

What if I bought a security camera and installed it in my bedroom. Would "they" take that too?