Battery cell upgrade

So here is what im trying to do, upgrade the battery on my laptop.

my laptop is a 6 cell 11.25v 5600mah, with two parallel circuits of three cells in series.

i plan on making it an 18 cell. i get about 6.5 hours without it but i take long trips where i cant use sockets for days at a time.

Heres my problem though.

1. mine uses 3.75v 18650's but they dont make those alot. so is it safe to use 3.7v since they have 11.1v batteries that are compatible with my pc (asus u81a)

 

Yeah, that's not a problem.

 

That's really odd. I think you'll put a bit more strain on the existing batteries and they might wear/charge differently since they have different nominal voltages. A word of caution though: when I made my 18 cell I could not get my battery's chip to recognize that it has more capacity. I've cycled it several times now with no improvement. It's a long story but you won't have accurate battery reporting other than voltage if your chip is the same as mine.

EDIT: Nominal voltages aside you might have a more serious problem if the max voltages are different. Once you get up to like 4.2+V per cell, you really start killing the long term life of the battery with every tenth of a volt you go up. So you might end up with an 18-cell battery that doesn't last more than a year.

 

I would hope he would be replacing all the cells. Also yes, some brands lock their batteries which is very lame. But if say your brand of laptop does that, you can always buy a chinese battery in your country on ebay because those aren't locked. You will be fine. Just buy some good high capacity battery cells.

 

I plan on changing all the cells.

My basic worry is if the smart board on my battery doesnt recognize the lower voltage cells and wont work accurately.

And how do i know if batteries are locked? i have an asus brand laptop.

 

Locking batteries? I've never heard of that and don't think they could unless the batteries themselves have chips in them. My Asus cells do not.

Changing all the cells is a good idea since they have different nominal voltages. As a sidenote I am unsure if having the EEPROM chip lose power has any unintended consequences, so you might try swapping out a row at a time after normalizing their voltages (ie: make sure each parallel row reads within roughly +/- 0.1V max of one another, then swap out that row). I wouldn't want you to brick your battery.

 

with all of the effort (and uncertainty over it will even work!) going into this 18 cell battery project I would hope that the OP has also checked out the pre-built external batteries available. Many of them have solar and 12v auto charge options.

For long field trips I use a set of 120 watt NiMh batteries from Digital Camera Battery. Unfortunately, the maker has become very hard to get in touch with.

There are plenty of other options.

 

ive looked at external ones. the difference is that they dont last the smae amount of time per millie amp hour, i had one that said it was 25000mah that only lasted 3 hours and 29 minutes , but my 5600mah battery lasts 6 1/2 hours, i dont really get how exactly that works but there is a difference.

 

two other questions.

1. Is it bad to use protected cells in a laptop since they already have protection, i ask because im in the process of purchasing now and looking at wich cells to buy.

2. if it doesnt fit can i take of the protected nub/point/stub or shave it down or something.

 

tl;dr: Watt hours not milliamp hours.
If you're looking at mAh you should really do some more research before undertaking electrical stuff.

mAh is current delivered for a specified period of time at a given voltage (or voltage range). Take a look at a AA NiMH battery. It's 1.2V, 2000mAh. This means it can supply a total 2000mA (2 amps) of current for one hour at about 1.2V (assuming the battery is rated for that high of a discharge rate), or 20mA for 100 hours, etc. Realistically, you can expect batteries to perform closer to their rated mAh capacity with a lower current draw. So in the above example, you will realistically see less than 1h of use when drawing 2A of current, and closer to 100h when drawing 20mA of current. Not sure if I worded that well but I hope it kind of makes sense.

Anyways, with battery capacity you are looking for Watt hours, not milliamp hours. This is a common marketing ploy. A typical 18650 cell is 3.7V and about 2200mAh. Why does it have a similar mAh rating as a AA NiMH battery when NiMH has such a smaller charge density and is physically quite a bit smaller? Well here is where we look at watt hours. Recall from high school physics:

P = V * I

Power = voltage times current. Let's include time on both sides since we are dealing with mAh, which is really current times time. We get:

P * t = V * (I * t)
(WHr) = (Volts) * (mAh)

So taking our 18650 cell, we get 3.7V * 2200mAh = 8.14 Whr.
Looking at a AA NiMH cell, we get 1.2V * 2000mAh = 2.40 Whr.

So the 18650 actually has over 3x more capacity than the NiMH. Thus when looking at cells, don't look at just their mAh rating, look at their voltage also. A 5V 10,000 mAh battery isn't as good as a 11.1V 5,000mAh battery (since 50Whr < 55.5 Whr ).


------

To answer your other questions:
1) I bought protected cells and they were too big for my original casing. They're about 2-4mm longer than a typical battery, which adds up when you have 3 in series. The laptop has circuit protection already so save yourself the trouble.

2) Yes but that's a bit riskier. You can buy the cell protection chips individually actually, so you might consider doing the opposite (ie: buying nonprotected batteries and getting chips later if you need them).

 

THNX for the quick reply, I know a lil bit about electricity , im in college for it right now im just slow at times .


Anyways im thinking about these cells.

Samsung 18650 ICR18650-30A 3000mAh Li-ion Battery x2 | eBay

since there 3.8v i dont know if it is too much current.

SOooo, 5600mAH devided by 6(hours) = 933.33333333

3000mAH x 6(parallel circuits of cells in series) = 18000 devided by 933.33333333 = 19.285714..........

so thats 19hours and some minutes of run time or around that capacity.

 

P.S i + repped for all the help.

 

Not the cells, but the circuit board of the battery. Also it doesn't matter if it loses power.

Rip that crap off. The battery circuitry does all the protecting you need.

It's actually not a marketing ploy. It's the way people measure batteries. The voltage and current info are given. Listing Watt hours is just to simplify it so people can easily figure out capacity without doing any math. Try to buy ANY battery cells and you will never see Watt hours listed. It is simply redundant information. What really annoys me is when a laptop battery lists Watt hours and leaves out mAh or voltage.
------

Protected cells NEVER belong inside a laptop battery pack.

 

lol wow. I get 6 hours of runtime from my 18-cell battery. You have a much more efficient laptop! Hahaha. The cells you picked out seem a bit expensive but they're Samsung instead of a Chinese brand. 3Ah is quite a bit of capacity, too. That's awesome.
I ended up with these cells: TrustFire Protected 18650 Lithium Battery (2400mAh 2-Pack Gray) - Free Shipping - DealExtreme
They work great, though they're protected and I'm unsure of their actual capacity. They seem to be over 2000mAh though. If I were to do it again I'd get the unprotected cells:
TrustFire 18650 3.7V 2500mAh Rechargeable Lithium Batteries (2-Pack) - Free Shipping - DealExtreme

I know EEPROM is nonvolatile but I just wasn't sure if power loss erases anything.

I agree. It's better to decide if you want the protection circuit now rather than later. The existing charge controller already does pretty much everything the protection circuit could.

Yeah I guess for small batteries or power packs that output a consistent voltage it's not an issue. But I've seen battery packs with USB and laptop charger outputs that say "8000mAh." The 8000mAh refers to the USB output (5V) rather than the laptop output (19V). A lot of customers interpret this as a higher capacity than their current laptop battery and then get confused when their laptop lasts half as long as their standard battery.

They work fine. They just don't physically fit right.

 

Alright i ended up doing it. i found the cells in a part store and there in already. according to my laptop im getting 15 hours but im not fully conditioned yet. I have yet to rn out the 15 hours either so i dont know if thats accurate.

Next mod im going to do is add a usb port to it to charge things while my pc is off, might add a port to expand the battery if i can find out how.

 

Wow nice! Did you end up disconnecting power to the EEPROM chip?

For USB charging you might look into a car USB adapter and solder that in. They usually run on like 11-15V.

I have a car outlet hooked up via molex connector on mine. Definitely not the best but I had a spare molex connector around so I figured I'd use it.

 

Ill definately try that.

just got this to make it look more professional.

Amazon.com: InstaMorph - Moldable Plastic - 12 oz: Arts, Crafts & Sewing

It coms in 1-7 days.

after letting my battery completely drain im probably getting about 18 hours ( an hour and a half less then i estimated) but its still more then enough to stay away from sockets. Ill probably need to charge it every 2-3 days im guessing.

EDIT: No i didnt disconnect power to the eeprom, i pulled them out series by series.

Next im going to get an ssd and see what processors i can upgrade from.

My screen has spots in it so i want to find a replacement screen but apperantly they all cost 100+ dollars but ill still continue to mod my pc.

 

Erm, I hate to burst your bubble, but easily molded also means easily melted. That product is moldable at 150F, and I imagine malleable even sooner. The operating range for li-ion batteries tops at around 60c, or 140f, so you may find your casing loosening up over time as you continue cycling the battery.

 

Yeah, should really build the box out of polystyrene or ABS.

 

Yeah i recently thought about that but it ended up being after i ordered. I might put some pvc between the friendly plastic and the cells.