Josh-Daniel S. Davis (joshdavis) wrote,
Josh-Daniel S. Davis


While researching about batteries, I ran across this
"Myth: The old myth about not storing batteries on concrete floors is just that - a myth. This old story has been around for 100 years, and originated back when battery cases were made up of wood and asphalt. The acid would leak from them, and form a slow-discharging circuit through the now acid-soaked and conductive floor."

I was researching because I had a premature failure in my Thinkpad Li-Po ultrabay battery. In researching the part, many people have also.

The Ultrabay Battery is Lithium Polymer. It's a 1-year warranty. The warranty generally means at the end of the warranty period, 70-80% of the capacity of the battery is still present.

Li-Po, at 1C discharges, are rated for 200-550 cycles, and this one is rated for 1 year warranty. 1C is generally around 0.4A per cell. On this battery, current draw is 1.3 to 1.5 amperes and recharge with laptop on full brightness is up to 1.09A. Li-Po is 4.2V/cell, and the battery is 12.53V. This means 3 cells, so we're only slightly over the ideal current load. We're OK there.

Li-Po like to be stored below 50% (they're shipped around 40%). Leaving it out of the laptop is bad because it will be stored at full charge. Leaving it at half charge is bad, because then it's never ready for use. Well, we're screwed no matter what with this, but it should only equate to 1-2% loss per month.

Complete discharge (well, below 10%) greatly reduces the life. With this unit, in 6 weeks, it had taken 25 cycles. A cycle is going down past 25%. Hrm. I've only gone under 30% once or twice, and the main battery only shows 10 cycles.

Further research and testing shows that when not plugged in, the ThinkPad power subsystem will completely discharge the ultrabay battery before beginning to consume the primary battery. There's no balancing or dual use.

The primary battery is 84.24Wh when new, and the Ultrabay is 29.16Wh when new. This means, when the laptop hits 75%, the ultrabay battery is at zero. Each time this happens, it ratchets away capacity from the battery.

It's REALLY easy to hit 75% just showing something away from power source.

This is very bad design. The power board should switch between batteries to equally discharge them. Alternatively, maybe discharge one battery down to 30%, then hit the other to zero, then the last one to zero. SOMETHING to reduce the death-discharges on these.

Anyway, I submitted a comment to Lenovo on the web, and am sending a sheet back with the battery in the return box.

and had a max capacity of 68% (19Wh out of 29Wh max).
Tags: batteries, computers, evil, lithium, thinkpad
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