help, Rebuilding a better battery for no-name netbook.

that's going to suck, all the 4000mah batteries I see are too wide to fit into the battery case. but the 500-ish mah ones fit very well, but that's too low. any ideas how I can get this to work? thanks

hey, do you guys think I can hook up two 2000mah batteries in parallel and use it as a 4000mah cell? so I'll have 2x(2x2000mah) cells?

also, what's the difference between these 2 batteries? why is the lower mAh one more expensive? which one would work better for me?

I might just make a battery without the plastic case and wrap it in thick tape.

http://www.batteryspace.com/Polymer-Li-Ion-Cell-3.7V-3650-mAh----UN-spproved.aspx

http://www.batteryspace.com/highpowerpolymerli-ioncell37v3000mah4545125-10c111wh30adrainrate-ullisted.aspx

Thanks

Can anyone help me out?

Hooking up cells in parallel is safe. The cutoff voltage for the two parallel cells is a little higher than the cutoff voltage for one cell,  so your cells shouldn't burn out.

In the ideal case, all cells should be individually connected to the smart circuit (so they may charge individually), however, your laptop draws <1C current so the chances of the cells becoming unsynchronized after you've matched their voltages is minimal (that is, if you dump charge on a pair of parallel cells, it should even out if the charge rate and the discharge rate is slow enough)

As for why the lower capacity cell is more expensive, its because that cell is a high power cell. It's capable of outputting >2C current. In this case, its a 30A drain rate. Typically, 1C means xA where x = the capacity of the cell. So for instance, a 3000mAh cell can discharge at 3000mA or 3A.

You don't need a high power cell because if your laptop has a 4000mAh capacity, and it lasts say 4 hours, then it's draining 1A per hour, so if your cell is >= 1000mAh, it is capable of outputting 1A per hour.

Thanks for your reply.

Do you recommend me getting 2 3650mah cells or 2 4000(2x2000)mah cells?

also, do you think this battery has a flash rom on it? is it safe for me to desolder the cells first? I'm afraid i will desolder the cells as I try to solder the new ones on.

Looking at the picture you took, this is one of the chips i see on it: http://www.ti.com/product/bq20z70. I briefly skimmed through its datasheet. There are two things you need to be aware of: page 21 (2.2.3 Limit based protection) and page 41 (2.5.5 shutdown mode).

Looking at page 41, it seems like when the battery is removed, the chip should gracefully shutdown. However, page 21 warns of a polling scheme to detect read write comms and data issues. If the number of faults hits a cutoff mark, it'll completely disable the smart circuit. Because you won't have access to equipment to reprogram the chip, it's a crapshoot. I would try to solder on the new cells before i remove the old ones just to be safe (since you only have 1 battery pack and can't find any replacements).

If you were to solder on the new ones before removing the old ones, I would try to match the voltage levels of the new cells withthe old ones to prevent as much tendency for the parallel cells (between old and new) to transfer change/balance. The way I would try to do this is if you can still charge your laptopbattery, drain or discharge the laptop battery to match the voltage level of the new cells you purchase. OR you can charge your new cells (but that would require you to purchase a cell charger)

Looking at the picture you took, this is one of the chips i see on it: http://www.ti.com/product/bq20z70. I briefly skimmed through its datasheet. There are two things you need to be aware of: page 21 (2.2.3 Limit based protection) and page 41 (2.5.5 shutdown mode).

Looking at page 41, it seems like when the battery is removed, the chip should gracefully shutdown. However, page 21 warns of a polling scheme to detect read write comms and data issues. If the number of faults hits a cutoff mark, it'll completely disable the smart circuit. Because you won't have access to equipment to reprogram the chip, it's a crapshoot. I would try to solder on the new cells before i remove the old ones just to be safe (since you only have 1 battery pack and can't find any replacements).

If you were to solder on the new ones before removing the old ones, I would try to match the voltage levels of the new cells withthe old ones to prevent as much tendency for the parallel cells (between old and new) to transfer change/balance. The way I would try to do this is if you can still charge your laptopbattery, drain or discharge the laptop battery to match the voltage level of the new cells you purchase. OR you can charge your new cells (but that would require you to purchase a cell charger)

Thanks howard, I Don't feel like buying a cell charger, so I guess I would use 2 3650mah batteries. Since the label said 3800, how dangerous would it be to use the 3650mah battery? thanks