Long life rechargeable battery pack

[photogav]

Hello

This is my first time here, and I am a bit of a electronics newbee, so please go gently

I am currently researching a DIY project I would like to make and while the physical act of making it is within my realms, the powering is a bit of a mystery, hence my joining this forum.

I would like to make a long LED video light tube that is battery powered. All sounds simple enough so far, except the tube is to be approx 3m long (so will contain a fair few high output LEDs) and it needs to be battery powered. Not only that but each battery needs to last approx 2-3 hours for the work I have in mind.

So my question is what type of batteries do I need to look for?

Any help and advice would be greatly appreciated

 

[kellys_eye]

You need to know the actual power being used - then you can chose your battery (chemistry) and pack size to suit however long you wish it to last.

i.e. if your light takes 12W (same as 1A at 12V) then you need a 12V battery that can store at least 1A for one hour or 2 amps for two hours etc. A typical lead-acid battery (as used in burglar alarms) might be rated at 7Ahr which means it can deliver 1 amp for 7 hours or 7 amps for 1 hour.

In the example I mentioned (1A at 12V) such a battery would (in theory) run your lamp for 7 hours...

As ever, you have to take into account that no system is 100% efficient and allow for 'waste' therefore in a real world situation the 7Ahr battery would probably only last 6 hours (maybe 5 hours).

So - how many LEDs, what size/wattage are they etc?