Hi, I bought a new battery for my n810 but it doesn't work. The battery says BP-4L (for E71/N97). Even it doesn't mention n810, I thought if it is BP-4L it should work in n810 then bought it. It fits n810 well, and when powered on, the screen showed NOKIA then turned off (tried many times, it's the same). I charged the battery using an external charger. I suspect that the battery may be ok, but there seems be an internal circuit to check the battery. Since this battery is not a geniue nokia one, the OS may block it. I am just wondering if my guess is right? Or it might be something else. Thanks. BTW, the n810 works fine with the stocked battery.

Sounds like a dud battery, I would return it for a refund.

The battery looks brand new. I peeled the seal. I bought two, I'll check the other one. It's unlikely both are dud batteries.

I have been thinking about some ink cartridges that come with a chip so you can't refill or make a copy.

BP-4Ls have nothing like that, and all the charging logic is on the N810 side. I use a third-party alternative (mugen) myself without any problems.

I also bought a "for N97" battery and it works fine in the N810

I also have a 3rd party battery (a 'Pisen') on my N810 and it works just fine.

I remember back when I used a couple of third party batteries on my N900 and charged them with an external charger, quite often if I'd let them run right down to having next to no power left they wouldn't start charging in the external charger, or in other words I'd have to at least start to recharge them in the phone itself.

In my experience running a phone dealer not so long ago that happens with quite a lot of phones regardless of whether they're using third party batteries as well.
For example my old POS iphone, when it runs flat it needs to sit on charge for at least 30 mins before you even think about pushing the power button.
You'd be surprised how many people would bring their "dead" phones in to get fixed, then before sending them away I'd simply do as my example above, and I **** you not, they would start up as usual.

Just speculating here but I think this is why most phones turn themselves off while still having a small charge remaining.

So yeah, put the battery in your phone, let it charge for at least an hour before you try turning it on, and if it doesn't start then its probably a dud, otherwise it's just that it didn't have enough charge in the first place to start charging through an external charger, weird I know, but externals are just weaker like that sometimes.

I finally found the problem and it's a big surprise. The battery is good, but the size of the battery is slightly off. It is slightly shorter than the original one. So, when inserted, the three metal pins of the battery are not all tightly locked with the tablet. Seems, the tablet knows the battery which is why the splash screen shows up but feels something is wrong then shutoff. I actually used a multimeter to measure the voltage between the three metal pins and they are different. They are all required to be in good contact with the tablet. I put some tape and firmly push the battery, the tablet powers up normally.

This is a surprise! It's neither totally off contact nor tightly locked, I called it half contact. Hope this can give some one additional clue if the 3rd party battery has problem.
Thanks for all who gives the suggestions!
Cheers!