Handy explanation of battery capacity, especially at it relates to PDAs, linked for reference.
Amp hours or Ah measures capacity. That is ultimately what we want to know about PDA Batteries from a consumers point of view. Amp hours quantify how long a pda battery can deliver a certain amount of charge before it runs out. As with all metric measurements, Amps can be divided into smaller (or larger) units by adding a prefix.
In the case of PDA Batteries, a milliAmp hour (mAh) is most commonly used. Note that 1000 mAh is the same a 1 Ah. (Just as 1000mm equals 1 meter.) Note that Amp hours do not dictate the flow of electrons at any given moment. PDA batteries with a 1 Amp hour rating could deliver ½ Amp of current for 2 hours, or they could provide 2 Amps of current for ½ hour.
Typically, PDA Batteries will use 1 to 3 Amps per hour, depending on the model's processor speed, screen size, screen brightness adjustment, usage, and other factors.
Keep in mind that slight variations in voltage generally do not impact the performance of your PDA. We see this all the time with universal and external batteries. The original battery might be specified at 10.8 Volts, but customers using a universal part can operate their laptop safely at either the 10 or 11 Volt setting.
Converting Sony's watt hours to amp hours
Battery Capacity Conversion http://www.camerahacker.com/Definitions/Battery_Capacity_Conversion.shtml
Comparing capacity of different battery technologies
Tungsten T3 900 mAH
Tungsten T5 1300 mAH
Tungsten C 1500 mAH
LifeDrive 1660 mAH
Treo extended battery 1800 mAH
Palm Zire 31 900 mAH
Palm m500/505/515 850 mAH
2004 iPAQ 1800 mAH
Fujitsu-Siemens Pocket Loox 1640 mAH
Dell Axim X50v 1100 mAH
Toshiba e830 1320 mAH extended battery 2640 mAH