Thinkpads Forum

I wonder if anyone knows what range of power supply input voltages the Thinkpads are ok with. I'm particularly interested in the X40 and 240. The reason is I'm thinking of making a big external battery pack to use instead of the AC adapter, for extended operation without AC power. So I want to know if I really need regulated 15 volt power, or if I can use a 12 cell NiMH pack (10000 mAH D cells) or maybe a 14.4V lithium ion pack (= two 6-cell camcorder packs). Thanks.

I don't know about the X, but I had the same thoughts about the T42 which use a 10.8V internal battery, but its power supply is at 15V or 16V, I don't remember exactly. Anyway, I called the technical support, and asked them if it is OK to connect a lower voltage than the power supply, like a car battary which is around 12V, and the support man said that it is OK, and that I should just be careful not to connect higher voltage than the power supply rating. A lower voltage is OK, he said. So I guess that your external battery voltage should be somewhere between your internal battery, and your power supply DC output voltage.

I would be very cautious about varying the input voltage. ThinkPad adapters are designed to take a wide range of AC input and create smooth, regulated DC output for the ThinkPad. You need to take care of voltage spikes and voltage variations. Higher voltages are lethal to the ThinkPad and lower voltages can disturb sensitive circuits. It seems just easier and safer to use the adapter provided. ... JD Hurst

Batteries can not produce spikes. So in that respect they are safe. Safer than the provided power supply adapter, which can transfer a surge or a spike to the ThinkPad. Voltage variations? I don't think that it is even possible for a battery to go over its MAX rated voltage. Maybe the voltage could vary to the lower side, if the battery can not provide all the required current. But this could be known ahead by the battery power specs. It may be worth further exploration, but laptops has used both internal and external batteries for ages, and every battery gets empty once in a while, and its voltage, and current capability drops. I didn't hear yet about any laptop exploding over its empty under performing lower voltage battery. But that I didn't hear about it doesn't mean that it didn't happen... Be Warned!!!