My N900 was sold to me with a tired battery that barely made it to one day of very mild usage. Clearly this was unacceptable, so I researched aftermarket batteries - coming to the conclusion that everything available officially is either too weak or too expensive, and the only way out are homemade custom batteries.

So I decided to make one, but because I take to heart the saying "anything worth doing is worth doing to excess", I decided to make it on steroids.

Feast thine eyes, mortals, upon my creation:

Edit: dead links! Imageshack ate my pics and I can't be arsed setting them back up properly, so here's an imgur album.




IT'S ALIVE! IT'S ALIIIIVEEEE!!!

Ahem.

Those are three 18650 lithium-ion cells, of the kind used to make laptop battery packs. I rather doubt they have the stated capacity of 2.5 Ah, as they're Chinese cheapies (I paid about $3.5 each from DealExtreme); previous experience leads me to believe they should have anywhere from 2 to 2.2 Ah, but who knows, they might surprise me - it's happened before. I have a professional RC charger that I could use to test them properly, but with such a large pack it'd take a while and to be honest I just can't be arsed.

I'd like to find some sort of protection for the battery, but it has to be fairly resistant without making this thing even more bulky; I still have to think about that (I'll probably end up using cut-up CD cases).

Is it comfortable, you ask? Well, it depends; it's still pocketable, but whether you'll feel discomfort pocketing it depends on the depth of your pockets and how used you are to carrying lots of stuff in them. I'm used to that and I have fairly deep pockets (they're one of the essential parameters by which I choose my clothing), so I find the size and weight tradeoff to be acceptable, though a bit of a handful. Fashion victims with skintight clothing and/or tiny purses need not apply.

Runtimes? Theoretically about a week, give or take a day. It took two nights and half a day to charge the pack fully (the cells are shipped at 40% charge); since then I've topped it up at night and it makes it to the end of the day without dropping a single notch on the battery gauge.

A few more pictures of the mutat... er, modification process:



Lineup of the batteries, disassembly of original battery, JST connector soldered to battery PCB




PCB fitted then glued in place, setup tested with a spare 18650 cell.




Assembly and soldering of the big battery, melt-glued on the back casing, and a view of the casing's underside featuring the other end of the JST connector.

Edit: I'm no longer using my N900, but for the benefit of anyone who might be thinking about such a modification: three cells really are a bit too much. Since writing this the pack degraded into uselessness and I rebuilt it using only two 18650s of better quality (if I were to do it again I'd use Sanyos; 2.6Ah ones are fairly cheap on DX). It's now much less pocket-unfriendly and looks like this:

OMG it looks like a bomb made to detonate if you place a call...

Just kidding. Great job!

oh this is awesome it looks like an anti-air tank

hmm, i think screen size is not really proportional with size of battery...but looks cool enough

Heh, I avoided using really strong glue because I want to be able to remove the modification and use a traditional battery if I ever have to take it on a plane. Somehow I don't think they'd let me carry it onboard (or in the stowed baggage, for that matter) otherwise.

What do you mean?

That's completely obscene. Loving your work!

Great work!
Looks like a Time bomb

Are those batteries really 2500mAh?

Exactly - I suppose it could go as far as you landing on floor, with someone's knee in Your neck (depending on where You live, in UK you have it guaranteed).

Otherwise, nice frankenstein addition to Your full-sized external USB port. if You're reading 3Ah battery thread (or my one about custom body replacement), you probably know, that using 2x 18650 is my plan (although, I'm thinking about phillips 3Ah or 3,8Ah ones, resulting in 6Ah or 6,8 Ah, respectively). In my case, I would put them inside body

It would be great, if You could measure capacity, either by RC charger, or on device itself (as per link in my signature). dr_frost_dk, if You're reading this (I know You will, sooner or later), maybe it's good idea to add link to it, into 2nd post of battery thread, in "other users mods"?

/Estel

As I said, probably not; Chinese batteries are usually overrated, with very few exceptions. I've used grey Trustfires before, and I've found them to be anywhere from 2 to 2.3Ah (that is, 2000 to 2300mAh) depending on the phase of the moon.

I should mention that Ultrafire are a more known brand, but they cheat a lot more on the stated capacity and actual quality of the cells. I'm a member of the CandlePowerForums board as well, and many users there have conducted extensive testing of Chinese Li-Ion cells; Ultrafires consistently disappoint, but Trustfires have come out as a good bargain-basement choice. They don't have the capacity or durability of Sanyos or Panasonics, but at $3.5 a pop it's a compromise I can make.

I could always just bring my backup phone (unmodified Motorola Droid 2 Global) if simply going on a short vacation; I wouldn't have mobile data anyway, which limits the uses for a smartphone, so I could stomach going back to Android for a few days.

Problems would arise if I were to stay somewhere for a few months... I'd carry the N900 with a normal battery and either backless or with a replacement back casing, but I'd want to carry the big triple-barreled monster at least in the suitcase so I could use it at my destination. What's the proper procedure? Do I go to the security people and say "look, I've got this battery I have to carry with me, but I need you to see it now so you don't think it's something entirely different"?

I doubt there's such a thing as a genuine 3.8Ah 18650. Last I heard the big guys (Sanyo, I think) had just barely managed to make one that held 3Ah, and even that wasn't being sold in great numbers; I'd be surprised if a 3.8Ah 18650 could even be made with consumer-level technology.

I like the idea of a proper body, and if I had a 3D printer I might try to make one, but as it is I'll just slap a square of plastic on the whole thing and call it a day. I just want something else than the bare cells to act as a contact surface and bear possible impacts.

My RC charger only discharges at 1A maximum, but since I used relatively thin wires even that'd probably drop some voltage along the way. I'd have to discharge at 500mA, which would take most of a day. Maybe one day I'll do it, but don't hold your breath.

I'll give a look at the app in your signature.