I recently replace my battery in my i3 Toshiba. I don't remember exactly how old, but I'm guessing the original was 5 years and I was getting less than 1 hr out of it. I bought the replacement from eBay, and you have to be careful when searching. IIRC, I searched using the battery model # + the word "genuine". The first search result was
THIS. NOT a genuine Toshiba battery, but a genuine battery, as opposed to a fake battery I suppose. Anyways, found one from what seemed like a reputable seller
(LINK) and while the battery life isn't anywhere near what it was when I first purchased my laptop, I can at least get 2+ hours out of it without tethering myself to an outlet.
BTW, I too made the jump to W10 a few weeks back. Had a few problems originally, mainly not having scroll on my touchpad, which would have been a deal breaker. But, Synaptics finally updated their driver and all is well. So far, I like the OS.