Type of Batteries I need

[pathrunner]

Hi all, I'm a newb on this and am trying to figure out some math. I seem to be running into a wall. I'm converting a small module to run on batteries and am trying to figure out what size rechargeable batteries I need for 3 hours of run time. Operational power consumption is 13watts

Any help would be appreciated.
.

 

[kam1787]

AH is the amperes per hour rating that should be given with the battery specifications

So we need the current [amperes] to say. You only gave the watts. If you give the voltage, then we can determine the current it uses, and then the AH

 

[KlausST]

Hi,

13W with DC means 13 VA.
Multiply it with 3h then you have 39VAh.

Now you have to divide it by the voltage of your battery.

Example: 6V battery..
39VAh : 6 V = 6.5Ah.

But you need to add some overhead, because usually you won't go to the limit, the specifications have some tolerance, the battery will become weaker with time, the efficiency will be lower than 100% .......
I'd use at least 150%

Klaus

 

[pathrunner]

Been testing out batteries now for the last couple of weeks now. I have two bridged 18volt drill batteries and I'm getting about 2.5 hours use out of them. Not to shabby but I was really hoping to be able to get to that magical 3 hour mark. Wondering if I make the unit self charging I may be able to add s 3000mAh 3.7v and make up that 30 minute difference.

Going to have to find a battery source for custom batteries before I can get this project off the ground though.