I have an old Toshiba laptop (pentium 4) whose battery just crapped out. Looking at the battery, it says it's a PA3251U. Looking online, this thing is going for about $100! I don't want to spend probably 50% of this machine's value on a battery replacement!

My question is: what makes a laptop battery specific to a model? Do I really only have this one battery to choose from, or can I look for any battery that matches some certain attributes (like number of cells, voltage, etc)?


It's about the physical shape of the battery pack. Other than than, it's the voltage that the back can provide (and the maximum amps as well I suppose). Inside the battery pack are standard battery cells that can be purchased cheaply. It is possible to open up the pack and replace the cells, but it's not easy or completely safe. See this question.


The battery unit form factor (and the battery compartment design of your laptop) usually govern which batteries can fit. Besides the pin-out of the batteries may also vary. And, so might the electrical specs.

You can take a look at this LaptopBatteriesWorld page for Toshiba.


Laptop batteries will not just be a collection of cells. In general they also have at least some intelligence, from an overcharge protection circuit to a usage counter.

You might be able to replace the cells in the battery, but just soldering together cells to match the voltage won't generally work.

There may be third-party batteries available for popular laptops at a somewhat lower price than OEM.


Typically, they just try to cram as many Lithium Ion cells into a certain shaped package as possible.

The only thing that makes them unique to a model is the enclosure.

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If you do not mind doing a bit of soldering / using strong special tape, you can buy replacements for a fraction of the cost (warning - The cells can explode if they get to hot, so be very careful!)

Personally, if I need replacement battery packs, the first place I look is eBay.

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