Guide: replacing and upgrading laptop batteries

Discussion in 'Hardware Components and Aftermarket Upgrades' started by t456, Dec 29, 2015.

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  1. t456

    t456 1977-09-05, 12:56:00 UTC Moderator

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    Aim:
    • Replacing the lithium-ion cells inside a battery pack.
    Advantages:
    • Lower cost vis-à-vis full pack replacement (roughly 25-50%, ymmv).
    • Increased capacity vs. the original pack (from +21% up to +55%, depending on original).
    • Environmentally friendly (or 'less not-so', rather).
    Disadvantages:
    • Time
    • Burning down the house
    Tools:
    • Soldering iron
    • Multimeter
    • Box cutter or rotary tool (dependant on pack)
    Background info:

    Laptop battery packs may seem to vary from brand-to-brand and model-to-model. However, they all contain the same li-ion cells inside, either 18650-type (18mm x 65mm) or pouch-type, both 3.7V nominal.

    The main differences are:
    1. Type of cells; 18650 or pouch.
    2. Number of cells in parallel.
    3. Number of parallel cells in series.
    4. Total number of cells (x parallel * x series).
    5. Capacity of each cell.
    We'll elucidate the difference with a few examples along the way. Ah, and this guide is for 18650 types specifically. Everything applies to pouch type as well, but unfortunately pouch form factor is not standardised, so hunting down matching cells is rather tricky.

    Step #1: Draining the battery

    Run the laptop on battery until it has close to zero charge. This is just a precaution; it will minimise the consequences of the dremel/cutting operation. If you happen to cut/slice through the cell's container then it will short the cell's wrapped layers, causing a bit of heat/fire and such :vbbiggrin: . Really, just be a little careful, that's all.

    Step #2: Opening the pack

    If you're fortunate then it's a simple plastic clip design which can be pried open using nothing more than a screwdriver:

    [​IMG]
    [​IMG]

    Replacing these with 3400 mAh cells (highest capacity currently available) would increase total capacity by (3400-2800)/2800 = +21%. Cheapest stock battery pack, and the only one available, is $34.20 (using mere 2,200 mAh cells ... ), which we can compare to the alternative options:
    1. 4x 3,400 mAh cells for $33.00 -> +55% mAh, -3½% $
    2. 4x 2,800 mAh cells for $24.22 -> +27% mAh, -30% $
    So it's a win-win; save money and increase capacity at the same time. Of course, not all replacement packs will have less capacity than the original, but it is not uncommon, either; check the specifications before ordering any pre-assembled battery pack.

    Anyway, we're still at step #2, so let's open a two-halves-glued-together pack:

    [​IMG]

    This, especially, is where a drained battery is useful. The cells are very closely packed to the edge, so it's quite a small feat to damage them, thereby causing a short. The hot plastic can get a bit smelly, btw. Box cutter will not have that problem, but then you'd better have some bandages ready ...

    [​IMG]

    The white goo is normal; it keeps the cells firmly in place, preventing any rattling noise.

    [​IMG]
    [​IMG]

    This is an example of 2x cells in parallel and each 2-cell placed in 3x series. The advantage of parallel over a simple dual series design is that a failed or poor cell can be bypassed with its direct neighbour, saving the series. Disadvantage is that the parallel set will be as weak is its weakest member, since the lowest capacity cells will cap out before the rest and this will prevent the other cell(s) from charging to full capacity (maximum safe charge voltage is reached). If you can be bothered to make an accurate measurement of each cell you've bought, then it's possible to position them in the most optimal way:

    [​IMG]

    Of course, it doesn't matter where you place each worst cell within the parallel pack, as long as the worst ones are distributed amongst all four parallel sets. This specific configuration is from an M18x R2, btw, but many DTRs will be similar.

    Step #3: Choosing new cells

    First consideration:
    Batteries are a pain to solder properly, although you can get away with sanding the surface first. However, it is much, much easier to order cells that have tinned tabs soldered to the ends in advance (assuming they've used proper equipment). Cost isn't much higher, so unless you can't find cells with tabs for a decent price; don't bother.

    Second consideration:
    We want unprotected cells; most packs are cramped, so there's only room for true 65mm variety. The protection pcb adds ~2mm and those, usually, won't fit inside this casing. It is also unnecessary; the battery's control circuit has its own overcharge/de-charge protection. If for whatever reason you happened to have ordered protected cells then it's easy enough to remove the tiny pcb and wire (use knife/pliers).

    Third consideration:
    Order any capacity you want, just don't mix different capacities, used cells or brands. Of course, higher capacity (up to 3,400 mAh) will be more expensive, but not linearly so; entry-level cells generally have a poorer price/quality ration than their high-end counterparts. Mind that anything over 3,400 mAh is an outright lie and cells cannot be had for $0.95/piece unless they're either used (and re-wrapped with fresh plastic) or have 1/10th the capacity claimed. Expect $5 to $9 per cell, depending on capacity.

    In case you're replacing an x mAh cell pack with higher capacity cells; the battery pack doesn't actually know the capacity of the cells. It has a factory-preset Wh value in its firmware which is used along with current pack voltage to estimate the current charge level. This is merely an informational-type of application and is irrelevant to the charge cycle. What happens during charging is that the system (pack+laptop) will supply a variable (and increasing) voltage plus a fixed current (in mA). While it's doing so that will increase the cell's internal resistance due to the higher charge level. To overcome that additional resistance and deliver the same mA's, the pack will keep stepping up the variable voltage until it reaches ~4.2V, which is considered 'full'. At that point the charging current will taper off to zero (part of the protection circuit). With higher capacity cells it will simply take longer for the sets to increase resistance and, thus, voltage; charge time will be proportionally longer. The mAh/Wh report you'll see in HWiNFO or other tools will be wrong, though, since that information is part of the battery pack's fw. Consider lowering the %-left warnings to compensate for the increased life-span away from the socket.

    Step #4: Removing the old cells


    Use pliers to strip off the existing tabs; they'll separate easily from the cells. Optionally there'll be a few 'bypass wires' (or whatever they're called ...) interspersed in-between two cells or parallel cell sets:

    [​IMG]

    Their purpose is to speed up the charge cycle; one cell or set may overheat or be near-full, so a different set can be charged alternately. De-solder the wire from the tab and, optionally, make a simple sketch to remember where each was going (hence the different colours). If you got cells with tabs then you may disregard the existing ones; the new tabs should be long enough to bridge cell-to-cell and connect to the bypass wires.

    You may also run into this thing:

    [​IMG]

    It's called a thermistor, the purpose of which is to measure the cell's temperature and, in case of overheating, prevent thermal mayhem (slow down charging). After finishing the new battery pack simply reseat it snug against the replacement cell.

    Step #5: Soldering the new cells

    At last; the fun starts. With a parallel set it may be easier to solder each set before assembling the full pack:

    [​IMG]

    So I've just solder one cell's tab to the other's and plan to use the second tab for further assembly. Important bit here is that we want to test each set before soldering them together:

    [​IMG]
    [​IMG]

    Now, if our soldering job was awry then you'd find different voltages. Unless ... they just happened to have been identically charged to within 0.01V. Cross-checking the negative end of one cell with the positive side of the other would rule out that possibility as well; if the soldering joint was off then you'd measure no voltage whatsoever.

    Next thing is to assemble the sets and recheck total voltage (the sum of all sets):

    [​IMG]
    [​IMG]

    Looks good. Of course, you'll want to check in-between as well to make sure the bypass wires are connected properly. These too have soldering spots on the battery pack's pcb, so there's plenty options to check your work. With everything checked the pack can be re-assembled. Most likely it'll take a little force to get everything to fit (factory assembly is pretty exact), but if it's loose; consider a bit of padding with electrical tape to make sure the cells will stay neatly in place.

    Step #6: Re-assembling the pack

    With a clip type casing there's little to do, but the glued-on casings don't take a lot of effort, either:

    [​IMG]
    [​IMG]

    Pretty much lean towards one extreme end of the function vs. form spectrum (duh ... ). Use black/matching tape if the looks bother you ...

    Step #7: Testing the new pack

    Run something like Battery Eater Pro to confirm it's all working as expected:

    [​IMG]

    If you're smart, you'll make a 'before' and 'after' plot for comparison. Even better would have been a plot of the stock battery when it was still new and as it was used in your specific system configuration. Didn't do either, of course ...

    Happy tinkering :vbsmile: !
     
    Ashtrix, Vasudev, kosti and 6 others like this.
  2. Starlight5

    Starlight5 So what if I'm crazy? The best people are.

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    Excellent! @t456 so, bottom line changing the battery controller when reassembling is just a gimmick?
     
  3. t456

    t456 1977-09-05, 12:56:00 UTC Moderator

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    Indeed, there's no reason to as it doesn't know what cells are inside the pack. Think of it as filling a cup with an unknown volume; it will keep doing so until it reaches the brim. You might think it at least knows how much juice it has supplied, but this too is an unknown due to loss/heat.

    One reason to change it would be the Wh report to the OS, even if that has no functional consequences for the device. Could make it claim 500 GWh for example; it'd say '0% left' all the time, even at full charge. Not sure what happens with the cycle count value, though. This is a fw number that is used to estimate 'battery wear' and ticks off a cycle for each full->zero charge cycle (or 2x half, say). Yet, this too is a 'cosmetic' value, same as the Wh's. Perhaps there's a way to reset it to '0 cycles', but disconnecting the cells (cmos reset-ish) didn't do anything for my battery pack:

    [​IMG]

    Again; cosmetic. It charges to 75 Wh all the same, but if it bothers you then consider rewriting the firmware. A proper reason to use that would be to lower Vmax (maximum charge voltage). According to these test every 0.1V drop (-15% max. capacity) doubles the cell's lifespan:

    [​IMG]

    However, most laptops these days have a 'battery preservation'-type of driver, which does the exact same thing; limit Vmax. Funny thing is that the stock Vmax is really an overclock; one that helps sales by inflating the battery run time in the product specs. and reviews. Perhaps NBC could take that into account by listing the Wh + run time based on 4.2V charge, instead of whatever top-off charge the manufacturer has deemed appropriate.
     
    Last edited: Jul 10, 2016
  4. CWB32

    CWB32 Need parts for my flying saucer.

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    this may apply to the *usual* laptop batteries but the panasonic batteries have a part and design made of unobtainium that make cell replacement an exercise in futility .
    ... according to a couple of other members ...
    just saying that there may be some clarification needed at the beginning .
     
  5. t456

    t456 1977-09-05, 12:56:00 UTC Moderator

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    How so? They keep their stamina fine so far and appear quite genuine, to boot:

    [​IMG]

    The charge voltage is regular 4.2V as well, so nothing really special otherwise, save the capacity. Of course, they're not cheap, so any offer that seem too-good-to-be-true, likely is. Bought a rather cheap pre-assembled pack once; never again :vbeek: ...

    Please note that the guide is for soldering pre-tabbed cells, not soldering straight to bare cells. Wouldn't even consider attempting that without proper tools; move/shift once or twice and the connection breaks.
     
    Last edited: Jul 10, 2016
  6. CWB32

    CWB32 Need parts for my flying saucer.

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    i should have clarified this a bit better ...
    to the best of my knowledge , the battery packs for the toughbooks (say CF-30 , CF-31 , etc) contain a chip that must be re-written or replaced if/when the cells in the pack are swapped out .
    according (again) to a couple of members over in the panasonic forum (at this website) , no one has come up with a replacement chip or re-programing method (codes and software) .

    this has been a topic of discussion over there and i have asked the question myself .
    replacing the cells has been tried by other members and it was a failure .
    it appears that the battery pack and the laptop *talk* to one another (i am betting primarily for safety) .
    as the panasonic packs are rather spendy , one can imagine that others have tried in earnest to thwart the design .

    this may or may not apply to other brands of comps and their respective battery packs ... however ...
    i am certain that panasonic/matsushita is not the only company to have *smart packs* for their products .

    again , i mention this only to help prevent the uninitiated from stumbling down the path of futility .
     
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  7. Shawn

    Shawn Crackpot Search Ninja and Options Whore

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    I have tried and failed at rebuilding a Panasonic battery pack. I am VERY experienced with electronics. Many forum members have tried recelling Tougbook batteries. They all have met with failure.
    The issue is that the chip is a smart chip similar to what is in an ink cartridge. Not only does it read the voltage and temperature of the cells, it monitors the usage hours / recharge cycle count. If you refill an ink cartridge without resetting the chip, The printer does not know the cartridge is full. Same thing with a Panasonic battery.
    Even with new cells, the chip THINKS they are old cells and will lock out the battery. You will not gain any runtime.
    You must reset that chip so it knows that they are new cells.
     
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  8. t456

    t456 1977-09-05, 12:56:00 UTC Moderator

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    Alright, thanks for the heads up, both of you :vbthumbsup: . Too bad it's such bad news.

    Fortunately, cycle count does nothing to my batteries; peak voltage and real battery life are unaffected by its excessive wear 'value'. Terrible shame about the Thoughbooks, though, especially considering it's Panasonic (gods-of-batteries, no less) doing this :vbfrown: . Thinking about that ... they are in dual business; laptops plus batteries ... Would be nice to find out if other brands do the same; the only other example would be Sony. Will pimp a 4 yr old, $200 HP (or something) next week with $50 worth of batteries, let's see how that goes.

    Hm, has anyone de-soldered the fw eeprom of a brand new battery pack, replaced cells later on and rewritten the stored, fresh .bin back to the eeprom?
     
  9. Shawn

    Shawn Crackpot Search Ninja and Options Whore

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    Do you have the eeprom reader and such?
    I have a CF19 battery that worked, but was so-so. I will donate it to the cause.
     
  10. t456

    t456 1977-09-05, 12:56:00 UTC Moderator

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    Yes, if it has a fairly low cycle count than it should help 'the cause'. Only need the pcb, of course, so envelope shipping is fine.

    Hmm ... actually ... even a used-but-usable-pack might be good, too; read rom on day x, wait/wear/cycle the battery for a few days, read rom again. The roms' hex compare should show the exact address of the cycle count byte. Can do that using my own battery easy enough, then run a battery life test on high% wear and, on the same day, one with the rom modded to 0% wear. Likely there's a fw checksum, calculating that for the mod may be the hardest part. Tempting, this ...
     
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