Blog – Dan Joannis

Hacking a Laptop Battery – Increase Runtime

Do you have an old laptop whose battery struggles to reach 30 minutes? I used to.

An aftermarket 6-cell pack would have cost me around $40, which isn’t expensive, but the laptop was old (circa 2006) and not worth putting money into.  I happened to have a fair number of Lithium-Ion battery cells “lying around”, and decided to upgrade my pack, not just with new cells, but with more cells.

This project was completed about a year ago, and I’m surprised I never posted it before!

Disclaimer!

The act of disassembling Li-ION battery packs is in itself dangerous. Lithium reacts violently with oxygen and water, both of which the air has plenty. Puncturing a battery can result in fire. Short-circuiting
a battery will cause it to heat up rapidly, eventually resulting in fire. Even soldering a battery will heat it up, and if you aren’t careful can also result in fire. Be careful, and be responsible.

1. The packs

I started with a near-new Toshiba pack, and my half-life Acer pack. I proceeded to open both packs, in order to get to the cells. They are always nicely glued shut, so expect significant cosmetic damage opening them.

I ended up with this. A bunch of lithium cells ready for re-organization.

Also on my desk were another set of 6 fair lithium cells. At this point, I realized how I could make my life easier. The red and green cells still had their tabs affixed, allowing easy soldering. The blue cells did not. Thus, it was decided I would add the green cells to the red pack.

2. Initial wiring

Laptop battery packs generally have their own unique wiring. Although they are nothing more than 3 series sets of 2 parallel cells (so 2 parallel cells, in series with another two parallel cells, in se…), the connections in between the cells are also connected to the circuit board.

The reason for this is balancing. No individual cell voltage can exceed the safe voltage (generally 4.2V). Over-charging Li-IONs can, you guessed it, result in fire. So, for safety the voltage of each parallel cell is monitored.

When making my connections to join the donor pack in parallel, I made sure to include the balancing connections.

3. Packaging

The first prototype cell was simply electric taped together, and enabled me to perform some initial testing. However, this would not do as a final product. Using some thick packing tape, and an empty prepaid credit card, I fabricated an enclosure and included the notches for locking the battery in place.

4. Battery life

Laptop batteries keep track of their capacity over time. A battery is able to tell you how much run-time is left, based on the capacity it thinks it has, and the current power consumption. You can see these stats in Windows with the program BatMon. In Ubuntu, these stats are readily available.

From this properties page, you can see the battery was originally rated for 44Wh, however had worn down to only 26.6Wh.

Fixing this takes time. The battery must be recalibrated, and it is possible some battery firmwares prevent the capacity from increasing (as batteries generally always decrease). In my case, after several weeks of use, and several brutal full discharges, the meter recalibrated:

It now reports over 68Wh! It now has 150% the capacity of a new battery. The run-time reported is also much more accurate now (in the ball-park of 3h30). In fact, I performed a run-down test a week ago, and it lasted for 4 hours and 14 minutes, streaming 720p video over WiFi, full screen, but with sound muted and lowest brightness. Not bad at all.

5. Was it worth it?

… to save $40? That depends. For perhaps $50 I could have bought a 9-cell battery, which with brand new cells would have more capacity than mine. I would have even more run-time, and it might actually pass through airport security.

But I wouldn’t have this story to tell. And believe me, people ask about it when you use it. It is a ridiculous battery, and it actually works. Well, most of the time…

Tags: battery, hack, laptop, li-ion