Hello,
i am planning to set a T43 from pieces I've got (actually I am ready to assemble up to 3 of these from what I've got), and the idea is to set it for the best battery life.

#1 - XGA display, as it consumes up to 25% less power, and until LCD consumes about 33% of overall power needed by your laptop, it is a thing that matters much.
#2 as I hardly ever use my DVD drive, I am planning to swap it with bay battery. Adds almost no weight, lots of bettery life, and with a 52Wh 6-cell it can do as good as 9-cell battery
#3 Processor - as CPU is second after LCD power-consuming monster, I was thinking of getting a 2,26GHz Pentium M and underclocking it. Less power consumption, less heat (and even more battery life due to low temperature/low fan speed needed) but still very good performance. And here comes a question: will voltage of the CPU be even lower than normally when speedstep changes it to minimum?
#4 GPU - I guess the best way of getting things to work is to put a R52 non-ati mobo inside the T43. Cool and quiet, and not a battery hungry thing.
#5 HDD - and here are my questions: Is a SATA mod good thing in such case? Is it actually possible on R52 mobo to do such mod? As far as I am cocerned a SATA HDD(0,6-1W idle/1,5-2,8W working compared to 0,7-1,6/1,7-4,6) consumes less power, is cheap&fast. I should also try a SSD, but have no idea if it consumes less power. Some info about that will be useful, as I can spend some funds for such project.

Would be happy to see any comments or advice. Hope it will get working soon.

#1 if you say so...
#2 not quite but getting close to the life of one 9-cell.
#3 no idea
#4 OK, no problem
#5 SATA mod is the best thing after sliced bread. SATA drives are then a better choice rather than SSD, due to price/GB difference.

You're better off undervolting a PM 750 or PM 760, which will cost *way* less than PM 780 (unless you have one already) and still be perfectly capable of getting the job done.

If you're happy with XGA, you can use an Intel-based T43 planar (from models starting with 187x) and enjoy...

SATA mod is a thing of beauty.

Generally, I believe that T43 is a wrong platform for this type of battery-saving experiment, but wish you luck with your projects regardless.

T43 without UltraNav is perfect for a power saving build. Forgo the touchpad! That will use so much less energy than, for instance, a T60 with the more modern Core processors.
(Sarcastic.)

Seriously, I think T43 is fine for power saving. Use a single piece of memory for another little load reduction.

I have got almost all the parts, including the PM780. The only thing is actually an intel mobo (found one from R52 of ebay-like polish auction house, but otherways - unreachable).

I know that regarding a 14,1" models T60 would be a WAY better choice (not to speak, like, T400), but I have got almost everything for a T43 assembly as well as:
1. a whole lot of batteries
2. a fulldock
3. loads of replaceble parts (hinges, kb's...)
4. most important - it's my beloved T43, and after a little upgrade she will be my good travel mate.

Actually never thought of one brick of RAM. TY, that will help a lot.
Well, getting the mobo, starting the job. Thanks for the HDD option help. I believe the mod is possible for R52 as well?

Okay, got all the parts I need. Now the thing that is most difficult of all I think - the SATA mod.
Does anyone have some advices/learners how to do it? I already have things coupled in my mind, the only thing is - where to get the power from? Some pics should be great.

Sata mod: viewtopic.php?f=2&t=94308
It's most important to take your time, and you need a VERY steady hand when you remove the SATA chip.
Make sure to cover all the mobo (both top and bottom) with several layers of tinfoil (aluminium kitchen foil) before you start, leaving only a small square open for the chip and on the bottom under the chip.
First heat up the bottom of the mobo (under where the chip sits) to about 200 Celsius.
Then turn over the mobo and heat up the SATA chip to 250-260 C.
Use a sharp implement (such as a dentist's toothpick) to lift up one corner of the chip and then 'flick' it off.
Have fun.

What power are you talking about?

5V+Gnd
Important thing is the fact I will not have much space - its a 14in model.
Thanks for advice, that will be VERY useful

In a 14.1" model there is the same space available as in a 15" model, they use the same motherboard.

+5V (+) connect to old IDE pin 42 (2nd left from the bottom)
GND (-) connect to old IDE pin 40 (3rd left from the bottom)

I performed a super battery life mod because I need it for tuning ECU's on cars, sometimes it takes a day and it is comfortable not ot be "wired".

I used R51 Intel mobo, 14.1 XGA LCD from T42, Pentium M 750 (1,86 GHz running on 400 MHz FSB = 1,4 GHz and undervolted to the max, works perfectly on R51 mobo), no modem/BT, disabled all ports except COM1 (soldered wires directly to MAX3243C and fitted COM port to optical drive travel bezel) and touchpad. HDD is Hitachi 5400rpm drive.
It really does have significant impact as with Panasonic 9cell (BM shows 11% wear) it holds laptop in work for around 7 hours. Note that the user interface program that I use (VemsTune) is medium in resource requirements (around 100 MB memory, CPU hovers around 5-8%).

I am really glad how it worked out and this way you can have many things on T4x series: looong battery life, rigid laptop and durability. Now I have to find a palmrest that does not have touchpad

Not sure how well T43 board can be made to save power but SATA mod definitely helps.

You soldered SATA Power wires directly to both components (NEP AJ8) and the other brown component? Is it also possible to solder the wires to the IDE pins 40 and 42 (formerly IDE Connector)?

Yes you can:
Pin 40 = Ground (as well as pins 22,24,26,28,30)
Pin 42 = +5V

T43 uses DDR2 SDRAM, which is lower-power than DDR1.

I am interested in your serial port mod. Did you take pictures?

The difference between DDR1 and DDR2 power consumption is way smaller than that compared between 855 and 915 chipsets

I did not take photos, but I can, it's just about removing keyboard (chip sits right next to memory slot.

I was foolish to assume, that simply because it is newer, the 915 uses less power that 855. By now I have encountered a few laptops with the 915 chipset. You are correct, it is a higher-power chipset.