Increase the Capacity (runtime) of Your Laptop Battery.





Introduction: Increase the Capacity (runtime) of Your Laptop Battery.

About: I'm an electrical engineer specializing in software. My hobbies consist of software, hardware, and design. I dabble with industrial design.

Is your laptop battery dead?
Is the runtime not long enough to get you through the day?
Do you carry one of those huge external battery packs?

This instructable is intended to show how one may replace the dead li-ion/li-poly cells of a laptop battery and how one may increase the capacity of the battery by adding extra cells.

The reason why adding extra cells to the internal battery is suggested compared to carrying around an external battery pack is that for the same amount of cells in an external pack, the laptop can run significantly longer if those cells were used internally.

Step 1: External Battery Pack? Rip It Apart and Never Think of Using an External Pack Again!

So what's the voltage rating on your internal battery pack?
What's the rating on your power brick?

Lets use my tablet computer as an example.

The battery pack is rated for 3.7v * 3 cells or about 11volts. However, the power brick outputs 20v.

I've bought external battery packs before and have calculated how long it should last using watt hours instead of amp hours. However, that was wrong. The battery pack would need to output 20v in order to power my tablet, thus the battery cells used to increase the voltage does not attribute to the amp hours, which is indicative of how long the battery pack should last. Thus, a difference of 9 volts is significant. That's about 2 li-ion cells wasted just to match the voltage.

Another problem with using external packs is that the laptop would think that it's connected to an outlet, thus is not so weary of watching how much power it drains. The power brick for my tablet outputs 2.5 amps, thus it is possible at times my tablet is drawing 2.5 amps from the external pack. However, the internal batt pack only requires an average of 1 amp per hour.

So what would one do in order to increase the runtime of one's battery pack? Forget the external pack, just add more cells to the internal one.

Step 2: How Laptop Batteries Work

Laptop batteries are complicated pieces of equipment. They are somewhat redundant as well. There's a 'smart circuit' in the battery pack that monitors the conditions of the battery cells, however, it does not do what a lot of people say it does.

The image below is a typical smart circuit. It has four wires running out of it: ground, power, and two 'intermediary power' wires (actually the ground wire is just the tab on the right).

Lithium cells output about 3.7 volts. Like all batteries, in order to increase voltage, they are connected in series. However, charging a "pack" by adding power through the positive node and negative node of the whole battery pack is dangerous. They are not guaranteed to charge evenly (refer to resistance in series in a physics text). This means one cell may overcharge and explode, which is very bad especially since it's lithium. The intermediatary power wires are sandwhiched between every series connection of the battery pack so that it monitors each individual cell.

Now on to the nitty gritty. Most people would say not to mess around with the smart circuit, and they are correct. But if handled correctly, it won't be a problem. The core of the smart circuit does not control the charging cutoff and output cutoff when the gauge goes to 100% or 0% (older model laptops do, but not anymore). The smart circuit merely lets the enduser (laptop user) know how long they have before the battery runs out and let them turn on special options such as hibernation in order to save their work. Charging and discharging cutoff is done by a secondary monitoring circuit that monitors a one of two states called "end voltage" or "end amperage". So for those who believe that they must charge and discharge their batteries once a month or so to "recalibrate" the battery are wrong; it only recalibrates the gauge, not the actual capacity of the battery. That is, if one is missing about 20% of their battery capacity due to the gauge being offsetted, the only reason why one would need to recalibrate is because they want to utilize the hibernation/shut off option when the capacity reaches too low. If one were to turn that option off, one can use the battery pack until it drains fully, completely ignoring the fact that the battery meter is flashing 0% (Because the meter does not control the battery's cutoff point, just the computer's). However, if the li-ion cell is dead/dying, no number of charge and discharge cycles can bring the battery back to life; the cell is physically dead (so forget about the term 'digital memory loss').

Step 3: Parts List


Soldering gun
Solder (but of course)
fire extinguisher (somewhat a must depending on how careful you are)
alligator clips
dead battery
undead battery (zombie batteries) I mean, new lithium ion or lithium polymer cells (make sure you know which your battery uses)
duct tape (geek's best friend)

Other things as you see fit (second hand soldering helper, wire cutters, wire strippers, etc)

Step 4: Preparation/setup

Safety preparations

-put sand in can (picture below)
-place fire extinguisher someplace close

Battery preparations

-if you're just replacing your dead cells with new ones, obtain the same number of cells. As for choosing the capacity, bigger is better.
-Note how the cells are connected in series and parallel, and solder your new battery pack the same way.
-NOTE: do not remove dead battery cells from battery pack (explained later on)

-if you're increasing the capacity of battery pack, obtain nth times the number of cells in your battery pack (an original pack of 3 cells can have 6,9,12 cells, etc)
-for every series connection in the original pack, you can add cells in parallel. (a pack with 3 cells in series can accomodate 6 cells (pairs in parallel) in series. That is, two in parallel, and attach those pairs in series, etc) any number of cells in parallel is ok.
-NOTE: once again, do not remove the original cells from the battery pack.

My battery pack below has 3 sets of 4 cells in parallel, which are connected in series. (note: parallel groups are separated as left, middle and right. ) Wires are also connected so that I can solder the new pack to the smart circuit easily.

Step 5: Safety First: Test the Darn Thing

I've seen some people who've posted how-to's for replacing laptop cells immediately replace the cells seal the battery and use it. This is extremely dangerous, unless you want to cook your lap. The quality of the cells purchased is unknown, and needs to be tested. (manufacturers of laptop batteries quality test their batteries before shipping them off. And sadly, sometimes a batch can go undetected)

-So, attach alligator clip w/ wires to the new pack and bury it in the sand (don't forget which clip belongs to which wire)

-Here's the tricky part (yet another thing other how-to's messed up.) The reason why I said not to disconnect the original (dead) cells from the smart circuit (which I inadvertently did. Don't worry, it was my test battery) is because the circuit requires a constant power supply or the smart circuit guage messes up. You might wonder why worry about the gauge if it doesn't contribute to charge and discharge cutoff. This is because the laptop requires a signal from the circuit before the laptop will turn on (in case the cells are thought to be drained and draining more, even for a second can kill the li-ion cells. Or simply, something's wrong with the battery). So, connect the new pack to the circuit before disconnecting the original battery cells.

-However, what if you're using alligator clips, which is a temporary connection? How can you disconnect and solder on permanent connections? Either, solder on the new connections while leaving the clips connected, or you can even use a power brick with about the same voltage as the whole battery pack (a 11.1 v pack actually ranges from 12.68 v to 7 v so a power brick at 12 v is ok). But remember to add a resistor between either the anode or cathode of the power brick and the circuit, so you won't kill the circuit board. (Not connecting intermediate pins should be ok, I haven't tried. If you worry about this, you can reuse your dead cell as a temporary power source while soldering on the new pack.)

-Plug in the battery circuit into the laptop and place it FAR AWAY from the battery pack. Test the battery pack. Charge is first, then completely discharge it, then charge it again. This is when you should watch over the battery pack intently, because it might explode (sand should stifle the fire, but immediately unplug the battery from the laptop.) The fear here is the type of secondary circuit used to monitor end states. End Voltage type circuit is ok, but end amperage is no good. If you can tell what type you have just by looking at the circuitry, then you're in good shape, but if you can't there's always the fear of an explosion. From my experience, the circuit is typically end voltage.

Step 6: Completion

-If your battery doesn't explode/catch on fire, that means the circuit is good/the cells are good.
-Solder it permanently to to the circuit, and fit it back into the plastic housing if its the same number of cells, if not be creative and line the cells up so it fits nicely below/behind/etc your laptop. Use duct tape or if you have, shrink wrap it with rubber shrink wrap.
-And remember, be careful around rechargeable lithium batteries.

-Update: I forgot to mention. Depending on the type of "smart" fuel gauge, adding more cells won't change the 'estimated hours left' displayed by the laptop, this is because the number of hours might be a fixed range. One might think that even if it's a fixed range, the number of hours left or % capacity left might be proportional to the actual number, however, depending on the type of circuit used to count the "electrons" (some use ic's called electron counters), it might assume the capacity to be fixed as well, thus the estimated capacity won't be proportional, just truncated. However, from my experience, the capacity gauge stops at about 7%, until the physical battery drains until 7%, so it still effectively alerts the user when the battery is drained after below 7%.

-Update 2: At first I thought my smart board fuel gauge circuit was of fixed capacity, but after a few complete discharges, it recalibrated. Now it knows the capacity of my new pack and estimates accordingly (ranges from 9 - 8 hours total runtime depending if I'm constantly using my secondary hard drive accessed via USB and/or lcd backlight levels)



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    120 Discussions

    It would be nice if you would get straight to the point rather than waffling irrelevance. Somewhere in step 5 and 6 there might be an answer though it is presented wrong. The answer is to create a parallel battery pack. Though you waffled on for so long my brain almost went numb. You do not provide a schematic and do not present the answer with a scientific logical efficient teaching technique. You basically have not answered the question or shown what to do, you have written a complete mess.

    Chapter Two, One stage answer:-

    Take out the power lead that attaches to the INTERNAL BATTERY from the internal components, attach another lead from the internal battery to an external socket that has a switch that switches from the internal battery to an external battery when external battery is plugged in from the outside. Then attach the lead that is attached to the components, motherboard, ROM drive and any other parts that was attached to the internal battery and attach it to the newly attached external/internal socket from the inside side of the socket.

    Note, if your internal battery is attached to an external circuit before the power goes to the components then take the lead from that and repeat the same process. Do not detach the charging wires to the internal battery and unlpug the external charger when your external battery is switched on.

    For charging your external batteries, attach a switched charging socket to your external battery pack and charge each external battery one by one. If your internal battery has an external charging circuit outside the internal battery inside the laptop create the same type of process from it to another socket, a switched socket at the side of your laptop, and a lead from the battery packs switched charging wires to a plug on the side of the laptop. This is a process of rerouting.

    Remeber, you will need to mod your laptop to do this by cutting a hole or two in the side of your laptop and this will void your guarantee. If there is not enough room on the side of the laptop, drill some holes and leave the lead with the switch dangling on the outside, you will need the flat lead to go through a rectangular slot.


    You now have your internal battery attached to a switched socket from the inside to the outside of the laptop and when the battery is flat you then switch over to the external power brick that is plugged in from the outside. No risk of overpowering the laptop and no need to create parallel circuits.

    You can also do the same with multiple batteries and build your own switched power brick. This power brick would cost you much less to make than an off the shelf one. You could make one with twice the amp hours for the same price if you build your own enclosure for it.



    I'm assuming you have an A+ or similar type certification? Why not just do a search for re-manufactured laptop battery, isn't that the proper way that A+ techs work? Would cost you about the same in buying new cells hacking apart the battery etc. It is fairly easy to find outlets to temporarily connect power and swap out for a full battery. In fact will be much safer(Risk of fire/explosion/insurance etc.). Assuming you follow all of these guidelines, if you haven't shorted out the PDB on the pack and you haven't damaged the charging circuit in the laptop you're golden. But assume you temporarily managed to shock the PDB. It will no longer function and you can kiss your laptop goodbye! Most of these PDB boards have IC's that are proprietary, and illegal to hacking so it is best to either replace with a new PDB that matches your laptop or go through proper channels to obtain a new battery.

    I understand that laptops now have reduced battery life but for the most part a spare pack is as easy to replace than hacking apart an old one. Because once you take it apart you have to test each cell individually to test the charge capacity(Beyond the scope of this instructable). If any one of them is out of balance the whole pack is bad. Assuming you find a few good cells, do they match the capacity of your new cells? If not then the charge will always go to the least common denominator and that's the amount of charge given to your laptop. You are better off just buying a new one and not wasting time. Good Luck, Peace Out brothers.

    Motion Computing Tablet. I have 2 of those. They really are amazing and I recommend them to anyone who has a couple bucks and some time. They are old so not powerful but the screen is godly accurate for drawing and such.

    I'd like to see you take that through an airport and try to board a plane. Being red, it looks like dynomite.

    1 reply

    I did create a case for it so the red tape was hidden

    t is only dangerous if you don't know what you are doing. Laptop batteries can take A LOT before they actually become dangerous.. Shorting them out, or deliberately placing them in a fire or anywhere hot.

    If you want to Increase the capacity of the laptop battery,you could buy a 9 cells or 12 cells battery from here.

    Hi there, Unfortunately, I could not replace mine. It seems the contacts has been welded to the board. I do have a soldering iron. Could someone advice? Thanks.....

    4 replies

    I'm assuming the contacts are fairly long. If you have some needle nose pliers and perhaps something to wedge the contacts on the cell side, you can rip the contacts off of the cells. You can solder on wires to the freed contacts. If you can't rip them off, you can always cut off the contacts, but giving yourself enough contact space for soldering.

    Hi, thanks for the quick reply. I did try this the whole night only to find out the battery pack's board has to be troubleshoot/tested for failure and eventually the main powerboard on the laptop ...(darn!) Can anyone lead me someplace for troubleshooting the battery pack's board? By the way soldering lead and steel don't solder well, I ended up having a longer batt than the package... and reslodering...

    you need flux and need to heat the tabs a bit longer. I don't understand what you mean by troubleshooting. Are you saying the battery pack isn't working? If the smbus controller is dead (not powering the laptop correctly) you really need a jtag programmer and knowledge of the communication protocol to fix that, which isn't worth it. I would suggest getting another 'dead' battery and playing around with that. That is what I did in actuality. I got someone to donate their dead battery.

    Oh, well, it's too late for me now. I just missed the part where you have to keep power in the smart circuit.

    "smart circuit can't be disconnected from a power source"

    And the new li-po cells are just lying around since 2009.

    like all the good ones ( and win XP, 2K, Mac 10.6 ) they all get discontinued.
    i have a acer TravelMate C110, discontinued, needs a new battery ( not a no-name one ). but that's what ebay is for after all.

    Any reason why I couldn't use protected cells instead of unprotected? From what I've read about the protection circuits it doesn't sound like it would interfere with the charging/discharging process assuming I increase the total capacity.

    1 reply

    There are many reasons why it's a bad idea to use protected cells. For one, the smart circuit has two layers of protection: electron counting which gives you the estimated battery life, and the normal protection which handles extreme cases of overcharging and underdischarge. By have another layer of protection, you're going to confuse the electron counting part of the circuit, effectively (possibly) ruining the tracking and the laptop will never boot on battery alone if it thinks there's 0% left. The second reason is that the smart circuit was designed with the cells in mind; by introducing the protection circuit in the cell, you're effectively changing the design of the smart circuit. Unless you understand how the smart circuit works and have analyzed its function with the additional protection circuit, most likely something is going to be screwed up.

    Found this url on an EE page explaining the battery/charger requirements for laptops with some additional information included.

    Xeijix, Thanks for the detailed explanations. Possibly a stupid question or 2.... why 19volts input for a 11.7v battery charging circuit? (is the overhead used to pwer the laptop so charging and laptop operations can happen simultaneously?) Or is that entire 19 volts being sent to the battery charging circuitry?

    As the pwer brick supplies pwer to the computer, does the input simply split --with some current going to the charger circutry and some going to the battery? Is it possible to access that split and tie directly to the power feeding the cpu, avoiding the charge circuit completely? You indicated there is indicator message of some sort sent from the chargin circuitry to the computer regarding the state of the battery or "it won't turn on". Are all computers charging setup like the one you described here or are there differences such that I could have a recently mfg'd computer that would have a completely different charging circuitry design and function and your article would not apply to it? My Dell M70 (2005) computer runs with no battery in it. Is that bad for the computer? Does your description and explanation of the wasted cells in a 19V pack apply in this case? Where is the "extra" pwer gojng? Thanks for the very informative explanations, instructions, and the focus on safety!


    do u know where the 3 wires from the circuit board in a laptop battery go in correspondence with the battery series? i replaced the cells in my gateway mx 3560 battery, thought i remembered wher the wires went, but the battery will not power the laptop at all despite reading 62% charged. also they will not charge past 62%, leading me to think i have maybe 2 cells not wired correctly or 1 of the 3 wires from the board are not in the correct place. any help most appreciated.

    thanks, glenn.