Hi! My laptop battery has been decreasing it's capacity, and one year after I bought it the battery only charged to about 2000mAh, the designed capacity is 4400mAh(14.4V). So lately, and since I was dismantling my laptop anyway for some repairs and modifications, I decided to replace the cells (buying a new battery was way expensive). After some research(and some looking at the battery sticker) I found the cells were Sanyo UR18650F lithium ion cells. I'm pretty positive this is the model since it states in the battery is has Sanyo cells, the reference number contains UR18650F, and after some searching I found several sites pointing that those were indeed the cells used. After taking the battery apart I found it contained 8 cells, 4 groups of 2 in parallel and those 4 groups connected in series. This would mean that the cells were about 3.6V(14.4/4) 2200mAh(4400mAh/2). However on the Sanyo web page the UR18650F cells were 3.7V 2500mAh. The only reason I found for this was that the UR18650F had been upgraded, hence the [ UP ] next to the battery model on the Sanyo website. I'm pretty sure the voltage wasn't upgraded (just look at their lineup) and the difference might be due to the controller lowering the voltage from 14.8(3.7V * 4) to 14.4, but I don't know if the increase in the capacity would be well accepted by the controller and if it would allow the battery to charge past it's designed capacity(4400mAh vs 5000mAh) which leads into my next doubt. I also noticed the battery has some free space inside, which was enough for exactly 4 more cells. So I thought why not buy 12 cells instead of 8 and rewire them in 4 groups of 3 cells instead of 2. In theory, that would increase the capacity by 50%, a nice improvement. However, and since I believe the controller has no means of telling how many batteries it has, the same question reamains: would the controller accept this extra capacity and would it allow the battery to recharge beyond the designed capacity(4400mAh vs 7500mAh). So, all that I wrote boils down to 2 questions, based on your experience and knowledge do you think: a) the controller would accept equivalent cells with higher capacity, and charge them correctly? b) the controller would accept more cells, not increasing the voltage, just the capacity, and charge them correctly?(this kind of boils down to the same as a) If you can read through my poor english, I would really appreciate your help!
A friend of mine owns a battery company called Clear Power, I’ll run it by him sometime, but that may not be for a week or so. From my experience with nitro and electric RC’s I know that everybody runs their electric cars on 7.2 volts (6 cells) and they use anywhere from 3300mah, to the new lithium ion 4200, and 4800mah, and there speed controllers (cars computer) has no problem, and there chargers still stop charging when there full regardless of the mah. As long as the voltage is relatively the same, like, 14.4 – 14.8 is nothing to worry about, cause the laptop probably charges it with a clean 15 volts anyway (ex. rechargeable AA batteries are 1.2 volt cells, and are charged with 1.5 volt chargers), and if the battery is higher in voltage by a little bit, after a few charges it’ll end up turning into what ever the right voltage is. But I’m not a professional, so wait till someone else says something before you make a decision.
If the cells you replace them with are identical and you keep the number of cells the same it should be fine. Capacity has little to do with charging. Most lithium batteries are charged on a CC/CV circuit and when they reach peak voltage 4.1 or 4.2 volts the charger shuts off. Undercharging your batteries will not hurt but it will lower the voltage. I feel compelled to show you some problems with working with lithium batteries. www.rcgroups.com search lithium batteries exploding or venting. Trust me its bad.
So when you say identical, you mean same voltage and same charging behaviour, capacity is irrelevanst, right? On the Sanyo website they have this: Charge:1It-4.2V(CC-CV)(2.5hrs.) Discharge:0.2ItA(E.V.=2.75V). I don't exactly know what that means, but I'm guessing it has something to do with how to charge the batteries. Those specs apply to the hole cylindrical lineup, so if it is a Sanyo cylindrical battery it should charge the same way. And why do you say to keep the same nnumber of cells? Since I'll be rewiring the extra cells in parallel with the others, the voltage will be the same. Charging 1 or 2 or 3 batteries in parallel is the same thing right? Since the batteries are in parallel the final voltage is the same, when they reach peak voltage the charger stops, right?
you may have to keep voltage accross the Power circuit/Charging Circuit. I tried replacing the cells in my battery and remove the power compeletly from the circuit and the Circuit did not work at all afterwards it only lit up the bottom led charge indicators and nothing more. Also the charging circuit in those battery usualy have at thermister to keep the batterys from overheating when charged
Hmmm, I'l have to keep that in mind! I was acutally thinking about removing the power to the controller in order to "reset" it, but now I'm not =/
do you have any information on the charge controller. many of them only require pin strapping changes to reset max charge time and number of cells. If you leave it as it is, chances are you will not see the full benefit of the added capacity because the controller will stop charging before the cells are ready.
I think it uses a bq29310pw + bq9011dbt but despite my search efforts I couldn't find any info or datasheets =(
