Ok so you want a battery that would last a bit longer than your average lead acid battery.. Right... Get yourself the following :
1) an old /dead 7ah lead acid battery
2) couple of small hinges
3) a pull down latch hook
4) some 18650 lithium cells
5) some reasonably thick wire
6) couple of connectors
7) 3s ballance leads
8) and some tools to do the job, including a hacksaw, sodering iron ect...
VERY IMPORTANT PEOPLE! Please note that there are dangers to working with ang lithium cells, please dont bother with this build if you are not prepared to take the risk! The explode, hey burn down your house, they cause you to loose limbs... Bla bla bla... Go google the risks, and weigh them...
AT YOUR OWN RISK!
Ok Gary, with that out of they way, lets move on!
Step 1: Before Opening the Battery
Make sure the battery is dead! If not.. Discharge it completely... Please Gary!
Take the battery, and locate the small gouge on the top where you can lift the top part using a very small flat screw driver... See the red circles... This will expose the little rubber caps.. Remove the caps and drain any acid, and flush it as much as you can with water...
Step 2: Cutting the Battery Open
Battery must be discharged completely!
Cut the battery in a straight line right on the line where the top and bottom part had been glued together... Cut through the battery all the way...
This will leave you with 2 halves.
You can clearly see the one I opened was a fake.. It was full of glass!
Step 3: Level the Two Halves
I have not taken any pics of this step, but after cutting open, wash bothe sides after all the insides had been removed... Then put a piece of sand paper on a very level top, and sand the areas where you had cut untill the two halves fit on top of each other nicely without any gaps.
Step 4: Add Cells
Then add 3 cells to each compartment, ensuring that you solder all 3 cells top and bottom in parallel.. Those cells will then be connected in serries with the cells next to it untill you have a 3 cell battery in serries, that consist of 6cells each... See pics
Step 5: Add Ballance Leads and Close Up
Use the hinges and latch to close up after the ballance leads had been added.
You save more than half the weight and gain a whole lot of amp hours!
Hope you enjoyed this instructable.... :)