Battery: 10.8V and 14.4V?

[fixup]

Among my three X20 and X21, I see two types of batteries: 10.8V/3.6AH and 14.4V/1.8AH. Do X2* series use two voltages?

According to the manual, there are 4-cell and 6-cell packs. This confirms that battery can be 14.4V (4 cells) and 10.8V (2x3 cells). A strange thing.

[Terrahawk]

The 4 cell battery for the X20 series is a slim and light battery that does not protrude below the bottom of the machine. The 6 cell battery pops out a little bit and raises the front of the computer, which changes the angle of the keyboard.

I have a dead 4 cell battery left over from when I had an X20. It is a 02K6652 and has 4 cells in series for a total of 14.4 volts. Its nominal capacity is 1.6 Ah for a total energy content of 23.04 Wh.

The 6-cell battery that I sold with my X21 has 6 cells grouped in three lots of two, with each cell having 2.2 Ah capacity. This gives a nominal voltage of 10.8 volts and a nominal energy capacity of 47.52 Wh.

The 4-cell battery is noticeably lighter than the 6-cell battery and my old X20 with SVGA display weighed about 1.5 kg with it. My old X21 with the 6-cell battery and XGA display weighed 1.60 kg. In comparison, my current X31 weighs 1.67 kg with a 6-cell battery.

As far as I am aware, the circuitry in laptops contains a DC-DC converter with a fairly wide range of input and output voltages. A Li-Ion cell is nominally 3.6 volts (multiply this by th enumber of cells in the battery and you get the nominal output voltage - 10.8 or 14.4) and is charged until it reaches 4.20 volts per cell. This means that a fully charged 14.4 volt battery will actually show 16.80 volts at its terminals. 16.80 volts is higher than the 16 volts from the Thinkpad AC adapters. I have also seen my 4 cell X20 battery when it actually held a charge drop to just below 9 volts before the laptop shut off.

I guess what one could conclude from this is that the voltage supplied to the power inputs of a Thinkpad don't really mean too much as long as you don't exceed the maximum and minimum operating ratings. I do not know what the maximum limit for the DC-DC converter is and I'm not going to try and find out

[graywolf]

The X2* series seems fine with anything from 9 volts to 18 volts. Over the years IBM supplied several different batteries, some of them optional with combinations of 3, 4, and 6 cells in them, maybe an 8 cell battery too. The standard 6 cell battery was 3 parallel pairs in series. Your 14v battery was 4 single cells in series.

Just to make life more interesting the cells changed capacities over the years. Some are so similar that they will work with the same contoller in the battery, some need a different controller. I just noticed that my X24 has apparently been recelled as battery infomation reports it as a 4400mah unit, but the case says its 4000mah, of couse IBM may have upgraded the batteries at some point without bothering have a new batch of labels made.

I have a 4800mah unit on order from Hong Kong. I was hesitant but then figured the ones sold in the US are probably made in the same factory. Hope I am not going to be sorry for that thinking.