T4400 Battery Tips


A T4400C contains three (!) NiCd (Nickel Cadmium) batteries: Although the circuits within the T4400 that charge the two smaller batteries are very simple, in my experience these batteries never cause any problems. It is however wise to note that a machine that has not been used for quite a while looses its setup. Since the HDD type is always automatically restored the system will boot fine but you may have to reset some settings.

The main battery is the cause of problems. This battery, due to its rather rare square cells, is very expensive and needs to be treated properly to enjoy a long life. Basically it comes down to really use the battery (i.e. not using the system on mains power for too long) and use the machine on battery power until it enters AutoResume (i.e. until the battery is fully empty). The T4400C is a battery powered system so it should be used as such.

The above sounds easy. But still some of my well treated batteries broke down well before their sell-by-date. I have read a lot of literature about NiCd batteries and have come to the conclusion that one can treat a NiCd cell as the literature prescribes (such as no overcharge, always discharge fully before charging, no high temperature etc.) but that one simply cannot properly treat a NiCd battery that well. The problem is that within a battery there are a number of cells (in a T4400 battery there are 14) of which there is always at least one ugly duckling. This worst cell will for instance always deplete first or will always run hotter than the others. And since you cannot cater for the needs of this one cell seperately, it will die first. The stronger cells more or less fight against the weak one by almost certainly reverse polarizing it during a discharge (the discharge current from the other cells actually reverses polarity of a weak cell which causes havoc with the chemistry within the cell), making it even weaker.

An example; I have one battery that probably has one weak cell. If I could isolate that weak cell I could deep discharge and fully charge it a couple of times and that might strengthen it. But since it cannot be isolated I can only discharge the whole battery which means that the weak cell will be reverse polarized again and will grow weaker still, and charging the battery stops much to soon since the charger detects that 13/14th of the battery was already more or less full. There seems to be no way to do this properly. Overcharching the whole battery so that perhaps the weak cell finally will get a full charge has bad effects on the now heavily overcharged strong cells. Sigh.

The only cure is buying a new battery and (again!) catering for Toshiba's profits.

NiCd literature mentions that between the Ni and Cd electrodes sometimes a crystalline needle will form. I had one battery that appeared to hold no charge (i.e. probably one cell remained empty). I performed a very drastic solution by sending a couple of more than 10 Amps AC current pulses through the battery. It has worked fine since then. Not a cure for the fainthearted and not for all batteries. (Also a T4400's battery contains a fuse, so if the current is too high the fuse will blow rendering the battery worthless.)

A number of observations remain:
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