(be sure to check out the last step for some updated info and a how to for this method using 4 batteries, using four would increase the life span. i had to use three for the sake of saving space.)
hack that battery pack!! we have all seen those 4 double a battery holders sold at radioshack, online, etc. the following involves modifying that same battery pack. But what can you do to it? first before I answer that i would like to say that I needed to make this to meet a few needs in a small 8vdc booster circuit i made. The circuit can use a voltage input as small as 1.2 volts and amp it up to 8. So i needed a power supply, I was planning on using just one double a battery but the run time on that would be so short, also once the battery voltage drops lower than 1.2 it would quit working. It would last maybe two hours if I used one battery. SO after some thinking I decided to use a battery pack, but all 4 double a battery packs are designed for series wich would give me a higher voltage output but not a longer runtime, so I hacked my pack! with a few simple modifications I turned it into a series parallel battery pack. Whats this and why? If you havent heard of series or parallel before then I will explain the terms now. batteries that run in series outputs a higher voltage while maintaining the same mah as one of the batteries, some devices that use this set up are tv remotes, radios, flash lights etc. its where batteries are set up in a way where the positive terminal of one battery runs into the negative terminal of the next battery. Parallel however, now when you set up batteries in parallel you will have the same voltage output as one battery but a longer run time. So the batteries used in parallel would be setup with all the positive terminals and negative terminals connected. I know this can be confusing thats why I included a few pictures to show you what series and parallel look like(see next step for a look at the pics). Now this battery pack hack is modified to use series parallel. (you will notice I cut off one of the battery holders, turning the 4pack into a 3 pack) If you have a good understanding of parallel and series then you can probably figure out what both combined does. If not I shall explain! I hacked my pack to use two batteries in parallel then in series with one battery, so I am using two double a batteries in parallel while using another in series of the two parallel. this way I can have the voltage output of two batteries but the run time of three.
Update! Its been brought to my attention, if you use two batteries in parallel in series with two more batteries in parallel the performance would be better! see last step for a picture.
in short. Series creates a higher voltage output. (4 double a batteries would be 6volts. 1.5x4)
parallel creates a higher mah. longer run time (2000 mah per battery, 4 double a batteries is 8000 mah)
Step 1: Batteries in Series and Parallel
this is what series and parrallel look like. I made these pictures because I find it easier to understand something if you can see it.
Both of these setups are very easy to understand and are used a lot around the world.