Introduction: DIY: Increase Battery Capacity by Changing 18650 Cells

By Well Done Tips

This time I'll show you, how to increase lithium battery capacity or repair dead battery by changing 18650 cells inside battery pack.How I did it - you can check by looking DIY video or you can follow up instructions bellow.

For this project you will need:

Materials:

LG HG2 18650 cells,

Solder,

Tools:

Screwdriver

Soldering iron,

Utility knife,

Multimeter

Step 1: Begining..

I have this Bosch 18V 1.5Ah of capacity lithium battery from my cordless power tools. Battery isn’t working any more, so I decided to take a look inside and try to repair it if possible.
Inside battery are located 5 18650 cells connected in series. Each cell have 1500mAh of capacity. The idea is to upgrade this battery by changing all cells with LG HG2 18650 cells which have 3000mAh of capacity. So I’ll get 3Ah 18V battery at the end. The second reason of this upgrade is, that all cells are dead.

Step 2: Thoughts..

In this way I could upgrade 3Ah battery pack and will get double capacity - it will be 6Ah. But while this pack is performing very well - I’ll leave it as it is.

Step 3: LG HG2 18650 Cells

I’ll use high drain LG HG2 18650 cells with 20A of continuous discharge current and 3000mAh of capacity. Peak discharge current is rated up to 30A. At the moment those cells are best price, performance and capacity cells in market what I know. I want to notice, that for cordless power tools is needed high drain 18650 cell, with 10A or 15A of discharge current at least. All cells have nice and equal voltage, so there’s no need to balance them before assembling.
I got them from Gearbest.com if you want to get them too, here are links:

LG HG2 4pcs: link
LG HG2 8pcs: link

For those, who are interested in detailed battery specs I’ll recomend to read batterybro.com review article (link).

Step 4: Removing Ol Cells

Replace procedure is quite simple. There is need to remove old cells and install new ones.
I did my best by disassembling and tried to save old tabs which will be reused later.

Step 5: Soldering New Cells

Pretinned and soldered cells together. To make better contact surface for solder I scraped cells with utility knife. However, the best way to connect 18650 cells is to use spot welder. Because I don’t have one, soldering iron will do the job. Try do not overheat cells when soldering.

Step 6: Protection Circuit

All lithium batteries from cordless power tools are equipped with protection circuit, which is protecting cells from over discharge, overcharge, overheat and are counting the number of charging cycles. If any of those reasons triggered or damaged circuit - by replacing cells you won’t solve the problem. You will need to change protection circuit too. In some cases battery will operate, but won’t take a charge on regular charger. At this point battery could be charged and balanced with third part smart charger, like iMax B6.

In this battery protection circuit is minimal and have only temperature sensor. So there’s minimal chances that something will go wrong.

Step 7: Assembling..

Last check, does all tabs was soldered correctly. And look it was.
Assembled all together and put battery on charger to check, does it will charge on regular charger. Great, works as it should.

Step 8: Summary

Battery fully charged and performs very well. Old battery was binged back to new life. Plus now it have twice capacity than it had before. Great result for small investment.