Update: I had several problems with Mugen batteries, and now can not recommend them. In addition to the flaky lugs mentioned above, the capacity of my Mugen battery is not any higher than the Nokia battery, advertised claims to the contrary. And two batteries I've had were unable to survive a deep discharge, unlike the Nokia batteries.

Regarding capacity, here are the results from some tests I ran:



I used flip clock to keep the N810 awake, and browsed to a web page that I set to refresh every five minutes. As the graph shows, the capacity of the new "1800 mAh" Mugen, on two different runs, was about the same as the well-used 1500 mAh Nokia, which had been deep discharged on several occasions. The other 3rd party battery (magenta line) was marked 1300 mAh, and indeed it has less capacity.

(Li batteries gain capacity when used for a bit, so I ran the Mugen through a few cycles before and during these tests.)

The real problem, though, is an inability to survive deep discharge. When I first purchased a Mugen battery, I put it in the N810, connected the charger, and then tried to boot the N810. Well, this is a mistake. I figured it would run off the charger, but apparently during the boot process the charger is cut off, and there was not enough juice in the battery to get through the boot.

Too late, I remembered having the same experience with the Nokia battery when I first got the N810. It had to be charged up a while before booting, even with the charger attached.

But unlike the Nokia battery, the Mugen was unable to survive this treatment. It would not charge any more, either in the N810 (which refused to go into charge state) or in a third-party charger.

Mugen generously exchanged the battery. But the other week I inadvertently left the N810 with the Internet radio on, and ran the new Mugen battery down. That killed it.

This doesn't happen with the N810 batteries. If they run down, the N810 shuts off, I recharge, and they recover (although no doubt a bit worse for wear).

Mugen customer support has been responsive down the line. They said that the lugs work with all the other devices that take a BP-4L, but are redesigning them to work with the N810. However, they have not responded in almost two weeks to my report about the batteries dying after one discharge.