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Fantastic post. Many thanks for your time an information. Looks like this is the official product page for the T420s/T430s and the part I need:rkawakami wrote:Number inside the red circle identifies the pack as being for a particular model or models. AFAIK, the numbering system is arbitrary. The single "+" sign indicates that it's a 6 cell version, vs. the "standard" battery that does not have a "+" sign (usually 3-cell). The double "++" is for the 8 or 9 cell versions.
As far as the "best" place, the factory is the ultimate source. If you mean "cost-effective", then there's probably several sources: the factory Outlet store (hit-and-miss for what you're looking for and when they have stock), members here in the Marketplace, eBay (some very good deals can be had but you have to be careful) and online retailers (same advice as eBay).
edit: Finally found the Support page on batteries: http://support.lenovo.com/us/en/documents/pd012165
The 66-series batteries are not listed but if you do a little digging around you'll find this: http://support.lenovo.com/us/en/documents/pd013052 That document says that the 81-series replaced the 66-series July 2012.

Very cool. I shouldn't have any issues with the 81+ in the T420s?rkawakami wrote:Indeed. For systems that are 4-5 years old, the battery, if bought new from the factory, comes pretty close to a system (usually without a hard drive) you can get off of eBay at the same price. You can try the Outlet here: http://outlet.lenovo.com Select Accessories and drill down until you find, or mostly not find, like right now, the battery for your system.
There's a 81+ battery on eBay, sourced apparently by NewEgg, for $105 shipped. And another for $95 shipped. Both are stated as new.
Cool. You are spot on in the New Egg eBay store:rkawakami wrote:Based upon the factory description, 81+ is designed to work in T420s/si and T430s/si. So, no, you shouldn't have any fitment issues. Whether or not the battery lasts longer than the 66+ it replaced, I don't know. From reading the blurbs about both batteries, the only real difference is that the 66+ used Lithium Prismatic cells and the 81+ has Lithium-Polymer. My understanding is that they are basically the same thing. Both are rated the same (44Wh and 3.9Ah) so they should power the laptop just as long. Given that the 66+ batteries are inherently older, I'd opt to buy/use the 81+ packs whenever possible, unless the cost differential is so great (like 50% less) if everything else is nearly the same (number of charge cycles and first usage date).

Yeah. I found that out a couple days ago. I accidentally switched the batteries. It's gives a error message at boot.ajkula66 wrote:One thing to bear in mind: a battery from the T420s can not be charged in a T430s, while the newer battery can be charged in the older machine.
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