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Sony VAIO FW series laptop battery hack

I’ve been trying to find a battery solution for my VAIO laptop, as I like the computer but the battery is toast. I can’t find anything that isn’t made in China and requires some third party BIOS flash to fool Sony’s lockdown battery check. Since I haven’t been able to find anything I decided to risk just changing out the cells in the original battery.

I bought a battery from Amazon and of course it wasn’t recognized by my laptop. So I tore it and the original battery down. They are pretty similar. Just remove the cells from the new battery and solder them into the old battery. Since the cells will have a charge, be extremely careful when desoldering and soldering on the controller board.

After putting the old battery back together with the new cells, it was recognized by my laptop. I did a couple complete charge / discharge cycles, and got about 3-4 hours of runtime on the batteries. The only problem I am having is that the charging controller appears to be preprogrammed for a particular voltage level, as the battery percentage is always a little off and the battery status is always “charging”. It appears to be looking for a cell voltage level that the new cells never hit. I assumed that the algorithm would be adaptive but it appears not. I’ve done probably  ten full cycles now and the numbers are always the same.

*What I’ve figured out so far: the controller is a Renesas R2J240F10. It uses SMBus to communicate with the motherboard, which is near enough to I2C that I can use I2C to sniff the bus. However, without the chip datasheet I can’t do much with it since I don’t know how the data is mapped. I need the datasheet to be able to figure out what values to replace in the EEPROM.

**I’ve also figured out that the cells in the pack (SE US18650GR) are of the base type 18650 but 18650 must just be a generic specification because you can find a bunch of different voltages and chemistry for that number. Charge cutoff in particular would be important. I’ve measured the cells of both new and old batteries after resting for a few hours and they are within 0.01 volts. So I still don’t know whats going on, and not sure if buying the proper Sony batteries will help me either.

***I think the controller board itself is failing, since I put the original cells back in and they aren’t being charged even though the computer is reporting they are charging. Too bad I don’t have a schematic. I gave up and bought a used OEM battery.

Tags: Electronics