On thing not quite covered in the article is the impact of "undersized batteries" on battery life

The so called "memory effect" in NiCad batteries is largely a myth

the MAIN source of pain in rechargeable batteries is the discharge rate. Remember, a battery is generating energy by letting a chemical reaction occur bwetween two ionized components. This invariably results in crystal growth

The faster you let the battery discharge, the faster the resultant crystal growth. And if you remember playing with Rock Candy as a kid, the faster the crystals grew, the larger they were.

Unfortunately, the larger a crystal is, the more stable a bonding structure it is. Which means that if you discharge at a rate above the "ideal rate" for a particular battery, you will grow crystals that are large enough that you cannot re-dissolve them at normal charging levels. Shipboard systems for example provide an Overcharge rate to deal with this in Lead Acid batteries, but you can't do the same thing with a cell phone or similar device.

So what does this have to do with your old Sony phone? Well the older phones OVER Specced the battery capacity. Furthermore as a household phone, the marketing perception was that you wanted to give a more "solid hand feel" to the customer - which means a bigger battery - which also means more talk time.

But as we have become more and more obsessed with smaller sizes, battery sizes have had to come down. And while the efficiency of the CPUs driving these pocket miracles has dramatically increased, The basic physics of sending out a radio signal to a cell tower has not. So the rate at which battery power req. have dropped doesn't match the rate at which the size of the batteries has dropped.

Now engineers know this and play all sorts of games in mazimizing the discharge rate of these small batteries. BUT if your battery is getting warm during discharge or charge - be assured that it is being drained at a rate ABOVE its ideal rated discharge rate. And that just means a shorter battery life. And as the article CORRECTLY points out, there isn't much you can do about it