My Dell Vostro laptop (after about 2 years of use) regularly runs 2 to 2.5 hours on its battery. It is a powerful laptop.
I bought the Lenmar external battery to help me work on long-distance flights and to take to coffee shops, meetings, etc. (where I'm not sure I'll be able to find an electric outlet). I used the battery only once on a 5 to 5.5 hour flight from San Diego to Boston. And it worked great (so far) so I thought I'd tell you about it.
I used my regular battery till I had about 20% charge left. I plugged the Lenmar into the place where my power-cord normally goes. It quickly (within about 30 minutes) boosted my battery capacity to about 98%--all the time I was still using my computer. I didn't have to reboot like I might have had to do if I was switching laptop batteries. I unplugged the Lenmar and continued to use my laptop and had about 50% left of it's capacity when the flight attendant told us to turn off all electronics. In other words, I probably had my computer on for about 5 hours, and it's likely it might have gone on for up to 5.5 to 6 hours.
I don't know whether this Lenmar external battery will always perform this well, but so far, it's perfect for what I need it for.
1. It doubled my battery life.
2. It's about one-third to one-half the price of an extra computer battery.
3. It's reasonably small, a little smaller than an Ipad.
4. It didn't get hot (a little warm maybe).
5. It's easy to use.
6. It is better than carrying a second laptop battery because you don't have to shut down your computer to install the battery--you just plug it in. It is bigger than a regular laptop battery.
7. You can also charge your cell phone (I think at the same time, though I haven't tried that yet)
8. And it looks good too.
In its first use, the Lenmar external battery appears to be a real find. I had no idea external portable batteries for laptops existed--and there seem to be only a few on the market that can handle laptops.