My ThinkPad T42p has two batteries: one large nine-cell and one small SuperDrive battery. The second battery gives me more than an hour of additional battery life, even with wireless on.
The problem is that the two batteries are recharged serially. First the large battery is recharged, then the small battery. Anyone who has used a Lithium-Ion battery with a digital gauge knows that the last 1% of battery charge takes the longest. This behavior is not a problem with one-battery systems because there isn't a significant difference between 99% charged and 100% charged. However, with two batteries, I find my gauge gets stuck around 77% (large battery 99% charged, small battery 0%) for a very long time. It takes about 8 hours to fully charge the system because of this. Many days my small battery is never charged.
Has anyone else had this problem? I assume there's nothing I can do to change the charging behavior because of the design of the laptop. Perhaps I could locate a standalone battery recharger to charge the second battery in parallel. Maybe I can use Windows or the BIOS to switch the battery being charged manually. Perhaps someone has a brilliant insight into discharging that will obviate the need for these long recharge times. Any ideas?