Lithium-Ion batteries

I'm not sure about the ability to recharge any lithium battery - I would never attempt it unless expressly told that it is possible for a specific battery.  If you have ever witnessed a lithium battery fire, you'd never try it either - the speed at which it reaches incredibly high temperatures is truly scary. 

The Contax 167MT has internal lithium cells that are designed to retain your settings once the camera's switched off; it's reckoned they have a maximum life of 7 years and I've not seen a 167 being sold recently that shows signs that the batteries have been replaced.  There is somewhere a guide to replacing them; they require a lot of disassembly and some de-soldering; it was assuredly meant for Kyocera's technicians to replace them but as the camera functions more than adequately without them, nobody seems to bother.  My only concern would be a rupture of the cells which could cause damage to the electronics. 

The absence of memory in lithium batteries, unlike NiCad ones, has been a boon but you are right - why, for example, a motherboard on a computer can't warn you when the 2032 is on its last legs is a real nuisance.

It seems that cameras use different types of lithium batteries -- computers too -- but often don't tell you much about them, such as how long they usually last or how to replace them

The Samurai cameras use a 2025 which last a long time -- and I assume are not recharged by the large main 2CR5 battery. All the manuals only say is "if the battery icon continues to blink after installing a new 2CR5, bring it in for repair."

The Sony A900/A850 camera manuals however specifically states that the internal battery (looks like a 2025, sorta) is recharged by the main FM500H battery under normal use. It goes on to say, that if the camera is not used for an extended period, both batteries will need recharging -- recharge the FM500H (takes about five HOURS), then leave it in the camera for 24 hours (WITH THE CAMERA OFF) and the internal battery will be recharged by the FM500H. (Alternately, you can use the AC power adapter which plugs into the camera.)

So it seems that cameras with internal batteries do things in different ways -- and the consumer if often left in the dark! At least with MOST computers (not my Dell 8200) it's pretty easy to replace the battery. On the Samurai X3.0 it's just removing a small panel. On the X4.0, the bugger is soldered in place. On the Z & Z2, it requires substantial disassembly.

While some cameras will operate with a dead internal battery, many will not -- or with certain features disabled. I don't know of any PC computers that will operate without a good BIOS battery -- but I assume they are out there.