B&N Nook HD+ battery replacement

[un4tural]

So, the battery in mine has died(well in the process), so i need to replace it, or get a new tablet, but what's the fun in that. Now, i know what you're thinking hop online buy new one and just swap them babies out. Well, here's the annoying and possibly fun bit comes in, nobody sells the damn things that i can see.  7" model? have a truck load, 9" HD+, might as well be looking for water on the sun. this is what it looks like

it seems to be two LiPo cells slapped together, i haven't fully separated and disassembled them yet, as first i wan't to see if it's even feasible and worth pursuing, so here are the things I'm wondering about:

1. if i get a Li Ion cell to replace this, will it be cool with it or spit at me and call me names?

2. these are around 4mm thick maybe, I'm sure i could salvage some phone batteries or something of similar size, would the Li Po charging circuitry there work with Li Ion cells? because i doubt it'd be worth to build new one, which potentially wouldn't work right.

if it is worth looking into, i'd put in one big ass flat battery from some other tablet and just splice the wires, though i might need two cells depending on how the controller and cells are wired, to get it fully compatible.

Yes this thing is super slow, but it has a lovely screen to watch movies and read stuff on, which is pretty much all i use it to do.

[Srbel]

As far as i know, the only difference between Li-ion and Li-Poly batteries is that polymer ones have a bit bigger power density and catch on fire more easily. Charging method is completely the same.

Problem could be battery management electronics in that battery pack. It can just brick itself, if it decided that batteries had gone through certain amount of cycles. In that case, even if you put new batteries in it, it will not work. :/

[mikerj]

Looks like a new battery is available but will likely cost more than a new tablet by the time you've paid for postage and customs.

If you can find suitable sized cells then it should be possible to replace them, but you are going to have to very carefully cut the pack open without destroying whatever the wires are connected to.  There are 3 each of red and black which may be commoned together for higher current handling and the other two may be a thermistor.  If the cells are paralleled then you could just use a bigger cell from e.g. an iPad or other tablet if it will fit.

[un4tural]

alright, took it apart further, defeated all the stickers, this is what was hiding: http://imgur.com/a/P32hD

the 3 red and 3 black are soldered together on same point, which ought to make life easier. the little part i guess is for load distribution, MP44A. green wire is laveled ID on pcb, yellow TH.

the cells are around 3mm thick, whole package 200x85x3 mm.

would it be as simple as soldering the new battery to the what essentially is 4 different wires and pluggin it in? I'm assuming the little pcb is just for load balancing between the two cells, so the charging and protection is on main pcb presumably?

[kwass]

I found it for $35 here:  http://www.mengtor.com/product_show.php?category=904&pid=20117

That almost seems like a reasonable price.

[un4tural]

need to register to see what they charge for shipping to UK. I'm leaning towards modifying it with fresh cells or just seeing if i can find a similar one, i found this http://www.ebay.co.uk/itm/ASUS-T100TA-DK002H-Li-polymer-Battery-3-8V-31Wh-Model-C12N1320-/181986273418?hash=item2a5f3a288a:g:VhYAAOSwwPhWkRSm which seems close, i think i should be able to find something with similar measurements that i could mcguiver to work.

edit: anyone can think of 2.5-4mm thick 3000mah cells i could use to replace these? or a 6000mah pack in similar measurements? xperia tab S has similar sized battery but none cheap on ebay, lg g2 battery seems close but i think it's too thick, but hard to find anything that's worth going for that wont cost more than tablet is worth... :/

[mikerj]

the 3 red and 3 black are soldered together on same point, which ought to make life easier. the little part i guess is for load distribution, MP44A. green wire is laveled ID on pcb, yellow TH.

The MP44A is a single chip protection circuit that includes the dual MOSFET switches for charge and discharge, quite a neat device. 

TH is probably a thermistor with the other end connected to ground. 

ID is possibly some kind of battery identification scheme, but there are not other active components that I can see so a bit of reverse engineering required to see how that works. It might be something really crude like the pin is either grounded or open to indicate two different battery types.

[un4tural]

thanks for the information, i guess ill see to pick up two 3000mah cells and solder them onto the pcb to replace em, to make sure everything is honky dory. i think i can go up to 4mm maybe even 4.5 thick to make it extra tight, question is to find the right sized cells to replace old ones with...

anyone know phone/tablet batteries that are roughly right measurement? 85x9 give or take 5mm and 2.5-4mm fat? thats without the circuitry, just the cell.

edit: so far best finds seem to be
http://www.ebay.co.uk/itm/Genuine-Replacment-Phone-Battery-BV-4BW-4-35V-3500mAh-For-Nokia-Lumia-1520-/231681999365?hash=item35f152c205:g:vIIAAOSwQPlV742C  Size 94*68.5*3.8mm

http://www.ebay.co.uk/itm/Brand-New-High-Capacity-Replacement-Battery-Sony-XPERIA-Z3-3100mAh-LIS1558ERPC-/141818109021?hash=item2105049c5d:g:9IEAAOSwnH1WX2oM  79.05 x 60.26 x 4.26

http://www.ebay.co.uk/sch/i.html?_odkw=xperia+z+ultra+battery&_osacat=0&_from=R40&_trksid=m570.l1313&_nkw=LIS1520ERPC&_sacat=0   98 x 82 x 3 mm

z3 battery probably would be a bit too thick. while both nokia and xperia z ultra batteries seem to be rather larger, i believe i could trim some of that off by removing the plastic shielding and using tape etc.

[mikerj]

http://www.ebay.co.uk/itm/Tablet-PC-Battery-3000-mAh-3-7V-Polymer-Lithium-Onda-PIPO-Ainol-Cube-Etc-/111871215561?hash=item1a0c0b47c9:g:SeYAAOSw~1FUXA6v

http://www.ebay.co.uk/itm/3-7V-3000-mAh-Li-polymer-Rechargeable-Battery-Li-Po-Li-ion-407090-for-Tablet-PC-/251548284895?hash=item3a917237df:g:gQUAAOxy0bRS~hOI

[amyk]

1. Make sure that the two cells are perfectly balanced (measure with a voltmeter) before connecting them together, otherwise the one with higher voltage will try to charge the one with lower voltage without current limiting, leading to some "excitement".

2. Those connections are not soldered but spot-welded. This is done so that the cells are exposed to as little heat as possible. If you can't do the same, perhaps thin spring-steel clips to hold the tabs onto the pads would be preferable to attempting to solder them.

3. ID could mean "identification" or it could mean "Id" as in "drain current" --- the protection IC's MOSFET drains are connected to the bottom pad and it could be used to monitor the current.

[un4tural]

@mikerj the ultra Z batteries still come down cheaper, i don't mind stripping the protection circuitry that is included in it, plus sony over the generic tablet battery sounds like a better idea.

@amyk
1. i'll definitely check but i suspect they'll be pretty close bought together.
2. I didn't strip the plastic sheath off the battery, as it's probably all the lithium firemaker inside under it, but it just has the contacts coming from the cell, but i suspect ill overcome this hurdle when i come to it, I think i got good odds there being some sort of metal tabs already spot welded between battery and the protection circuit on the cells i'd purchase, so i could solder to those tabs without impacting battery at all.
3. i wont worry about this, it's something the little MP44A is reporting back, since ill keep that, only replacing the cells, it should work perfectly fine and not cause any issues. hopefully.

i think i'll go for ultra z pair of batteries, they come down 5£ a pop, so 10£ all in, same capacity as these, size should fit perfectly too, just slightly thicker, but there is enough room in there. those nokia cells only come form china, i don't think i want to wait a month for them to get here... those generic tablet batteries, i don't think are worth the risk, i've tested a few of the cheapo 1000000mah external usb batteries for charging phones, them cells usually have half of decent ones, at best, not to mention the claimed spec.

edit: got a pair of them ULTRA z batteries, will see where it gets me tomorrow or day after and post an update and maybe the magical journey of soldering 4 contacts and putting on some insulation.

[un4tural]

ok so, got the cells, stripped em, removed the two pretty much dead cells (reporting either 100 or 0%, last about 2 hours use, so 1/5th actual capacity left or something, it started to go down really rapidly a few months ago until now) soldered a few wires and the few contacts that aligned correctly together, a little nice thick insulation tape and then crappy paper tape (yeah i realized i didn't have any proper one for this use too late) and they work a treat. Cells had 0.1v difference so i just stuck them together, didn't seem to cause harm.

i did short the contacts a few times to cause a few sparks, by accident of course, luckily didn't pop anything or release any of the smoke and all electrons remained imprisoned for a happy ending. few joints look crap, either the station or the rather fine tips weren't quite enough for the few large joints that i had to make.

It is now all happy, will take a few cycles for the electrons to align, but looks good so far, indicating the battery % correctly in OS and charging alright, will edit the post for last update on this after i put a few battery cycles on it.

all in all cost me 10£ and a few hours work refurbishing these. the Sony cells fit perfectly, they're actually a little smaller, so i had quite a bit of wiggle room left.

thanks for the help guys.

http://imgur.com/a/QqihT