simple battery charger curcuit

[happysteve]

Hi all, first post.

I am making a backpack that plays music, its basically going to consist of a specially made wooden box, 2 car stereo speakers, a 25watt stereo amplifier circuit I bought pre made off ebay and a block of 8 x AA rechargeable batteries to provide 12v of power.

I want to have the batteries mounted permanently within the box as a pack and plug in a standard mains power adapter into a socket on the outside of the box to charge the batteries. I understand this will require some sort of battery charge circuit and this is where my knowledge falls down. Hence why I'm here now hoping someone might be able to offer me advice.

I'm hoping to get one ready made if such a thing exists simply because my time is limited but I am able to build a kit.

For information I'm basically trying to copy the units shown here: http://armne.ws/G19g but the guy who made them is no longer around to ask.

Any help appreciated. Thanks

[piratepaul]

The batteries will have a max current, just get a charger close but less than max current. (ebay)
Or get a solar panel and a diode for the rucksack.

Tar&stuff.

[Biomed]

At 25W 12V that's approximately 2A so your AA batteries aren't going to last too long, an hour at full power, is this enough?

Have you considered using a 12V sealed lead acid battery? They are quite heavy but something like a 12V 7Ah battery would last much longer and you could use a plug in charger like http://www.rapidonline.com/electrical-p ... rger-72474.