This mod was done on an Asus Z7100 series laptop (Z71V to be exact). But the theory behind this mod should work on pretty much any laptop, notebook or netbook out there. It worked out better than I ever expected.
Step 1: Open the Laptop Battery.
Open Asus Z71V Battery Pack (Model No. A42-M7)
I started mine by cutting into the seam at the corners of the battery pack with a utility knife. I managed to get a flat screw driver into the incisions I made with the knife and started to pry the case open. Be very careful to not push the knife or screw driver too far into the pack as you could damage the batteries or battery controller PCB. I pushed my screw driver in too far and knocked a tiny resistor off my PCB. Took me half an hour to get it soldered back on.
Once you have the battery pack open, inspect how the batteries are wired up.
There are Eight 18650 Cells. A red wire for the + end of the series and a black wire for the - end of the series. white, yellow and orange wires for the intermediary charging points.
14.8v and 4400 mAh (milliampere-hours)
After around 3 years of use, this battery had degraded to around 28000 mWh according to Notebook Hardware Control (NHC). It only lasted 100 minutes or less; compared to 3 hours+ of runtime I used to get.
You need to acquire more batteries. Most people will probably have to purchase new batteries but I had some used Dell laptop battery packs lying around that I could cannibalize. I thought I would try one of them out first before buying new batteries. 
I chose one that appeared to be in good condition, it was for a Dell Inspiron 2650 series laptop. It happened to have very similar specs to my Asus battery - 8 cells rated for 14.8v. I opened it up and verified that it was in good shape. More on this battery later.
The amount of batteries you will need depends on your current battery. Always add additional batteries in an even multiple of the original amount of cells. If you have a 3 cell battery, you can add 3 more, 6 more, 9 more .... if it is a 4 cell, add 4 more, 8 more, 12 more, etc.
Make sure the cells you buy provide the same voltage as the original cells in your battery pack are (usually 3.7v). You may go as high or low as you like for the mAh rating. The higher the rating, the longer the battery will last (theoretically). Some manufacturers exaggerate a bit on the mAh rating. Trustfire seems to be a safe choice.
Also, stay away from "protected" cells, as your laptop battery controller already provides protection. The cells with additional built-in protection can cause the whole battery pack to stop working early if the protection on one of the cells gets tripped.
I though it would be a good idea to make the secondary battery removable instead of hard-wiring it in. There is a total of 5 wires connect to the second battery, but I couldn't find any 5 pin connectors around so I used two 4-pin molex connectors and just removed the 3 spare wires from one connector. I salvaged these connectors from some old computer fans. These are the 'male' ends of the connector.
The soldering points were originally covered by tape to prevent any accidental shorts with the PCB.
A Dell Battery; Model# BAT3151L8. Note The "Do not disassemble" Warning :)
Most people probably don't have spare laptop batteries lying around, and you will get best results from new cells anyway. However 18650 cells are going to be hard to find at most stores and you will probably have to purchase these online. You can actually buy them for a very reasonable cost online from dealextreme.com, which is a huge online store with free worldwide shipping.
I personally like the Blue TrustFire 2500mAh 18650 cells and was tempted to try out the Red UltraFire 3000mAh 18650 cells.
Make sure the cells you buy provide the same voltage as the original cells in your battery pack are (usually 3.7v). You may go as high or low as you like for the mAh rating. The higher the rating, the longer the battery will last (theoretically). Some manufacturers exaggerate a bit on the mAh rating. Trustfire seems to be a safe choice.
Also, stay away from "protected" cells, as your laptop battery controller already provides protection. The cells with additional built-in protection can cause the whole battery pack to stop working early if the protection on one of the cells gets tripped.
If you are going to be using your newly purchased cells as a secondary external battery, you may also want a protective case to enclose them in.
Pretty much anything should work but DealExtreme.com has specially made 18650 battery cases for cheap.
For future expansion and portability reasons, I wanted the second battery to be removable.
To bring the wiring out from the main battery I melted a small hole in the battery case with a soldering iron.
I inserted the wires and cut them to length so that each wire could reach its intended soldering point.
The wires should be inserted before you start soldering them to the battery.
Carefully solder the wires to the existing solder points on the battery. I first attempted to solder the wires directly to the battery cells but the solder would not stick so I made use of the existing solder points and it is working fine.
This is the + end of the battery series, I labeled this solder point #1. The - end was #5. The intermediary points were 2, 3 and 4.
I placed the cells back in the battery case partway through the soldering process so I could keep the wiring as tight as possible. My battery case has very little room to work in so I needed to keep the wires as short as possible. Be sure to keep track of what wires you connect where, and mark the corresponding pins on the molex connectors.
All 5 wires soldered on. I labeled the molex connectors to correspond with which solder point they were connected to (You can't see this, they were labeled on the other side).
It is a really tight fit.
Before I closed the case I reapplied tape over these solder points.
I taped the battery shut instead of gluing it, mainly because this is much faster and easier.
Now would probably be a good time to make sure it still works. My laptop powered up fine, so now I am ready to work on the second battery.
As previously mentioned, I will be using an old Dell laptop battery. You will probably get much better results if new cells are used, but I already had spare laptop batteries lying around so I thought I would try them first.
The battery controller will not be used. It should be removed.
There is a total of 8 Cells; you can't tell from the picture but they are arranged in 2 parallel series' of 4 cells each. Exactly like the Asus battery. There are 5 wires a red +, a black - and 3 intermediary wires for charging purposes, blue, white and yellow.
The existing wiring removed and the 'female' end of the molex connectors soldered on.
I salvaged some more molex connectors from an old computer power supply. I cut these wires to length and soldered them to the solder points on the battery. I made sure to keep the wiring the same as I had done on the asus battery. Positive going to Positive, negative to negative, and each intermediary charging wire going to their corresponding locations. If the wiring is messed up in any way, bad things will happen. The best case scenario would be that it simply doesn't work. Worst case scenario - there will likely be fires and/or explosions. Do it right, I am not responsible for any damage caused.
To be safe I taped over the contact points like I did with the Asus battery.
This battery had much more room to work in compared to the Asus one. The project is almost complete, all that needs to be done is to close up the secondary battery and connect it.
I taped up the secondary battery and attached it with some stick-on velcro strips I picked up for $1.25 (which is actually the only money I spent on this project). It holds the battery on very strongly, almost too strong ..... I almost couldn't get it off again! 
The finished product.
At first there seemed to be no change in battery life, but after the 2nd rundown and recharge, NHC showed that the full battery capacity had increased to 36000 mWh. After the 4th rundown and recharge it had increased to 46000 mWh, after the 5th, 54000 mWh, the 6th, 61000 mWh, 7th, 69000 mWh. The battery sensor is still calibrating but I am now getting a consistent 6 hours of battery life! This is almost double what I got with a single battery when it was brand new.
6 hours of battery life from two old laptop batteries.
I believe the reason the battery life has increased beyond what I though possible is due to how some Lithium-Ion batteries work. The higher the resistance (amps), the lower the battery life (mAh). According to NHC, my laptop draws an average of about 17 watts from the battery. Watts = Amps * Volts. So 17w / 14.8v = 1.15a. With the original battery, The 1.15 amp load was divided into two 14.8v series (four 3.7v cells per series). This gave a load of 0.575 amps per series. Now the load is divided into 4 series of 4 cells each (16 cells total). This brings the load down to 0.2875 amps per series. I'm guessing that higher amp requirements caused these batteries to lose their mAh rating much faster than a lower amp requirement. With the amps now spread out between 16 batteries (0.072 amps per battery), this is allowing the cells to produce optimal performance. This idea comes from a chart posted in this thread (page 2). Note the results for the two 3000mAh cells.
I could be totally off on my theory, but whatever the reason is for the great battery life, I am very happy to have such great results.
Next project..... adding a third battery!
How will 24 cells work? 28 cells? I'm hoping to find out.
by sites.google.com
Hi there, very interesting mod.
ReplyDeleteI am trying to do a similar thing but adding anexternal power supply (I was thinking about an ATX power supplier for the 12V).
Do you know how to trick the circuits within the battery pack?
Many thanks in advance