I tried recharging my 810 using a car charger connected to a static 12 volt battery, but it didn't work and now my machine won't charge on the normal power charger.

As I see it there are two possible causes and two possible outcomes:

1 the car charger is faulty
2 the connection to the battery is not a good idea

Is there any reason why a cigarette lighter socket connected to a static battery should be any different from the one in the car?

The 810 still works normally so now I'm trying to test two theories as to what has gone wrong:

1 the battery is damaged or

2 internal charging input is damaged. (or both)

I've ordered a second battery and an external charger which should test both these elements.

Any thoughts on this?

Well, before doing that you should have at least measured and compared the voltage from a standard charger and the thing you put together.

another data point: A car's 12v "lighter socket" (or "accessory port" in non-smoking vehicles) outputs 13.8 volts. A fully charged 'stand-alone' battery outputs 13.8 volts only when fully charged. It may put out significantly less than that if it has been sitting for a while...

Was this a nokia car adapter or something you put together. N810 uses 5V I believe center hot - if it were a store bought adapter- I have one from Wal-Mart - all should have worked.

I am afraid that you put 13.8 volts into the tablet and likely did damage to the charging circuity. I hope I am wrong.

There's documentation here for the 2mm charger; I don't think 14V from a car battery is likely to harm the N800.

BTW, if you make your own charger, and know that you won't use an accessory between charger and N800, check the accessory output spec (Figure 11) -- a 9V battery with an 8.2 Ohm resistor will work, with battery voltage up to 9.3 (fully charged), down to about 7.2 (each cell drained to 1.2 V). (This is a violation of the charger spec, but is guaranteed to work with any phone, N8x0, etc. that follows its end of the spec, as long as you don't use an accessory.)

http://www.forum.nokia.com/main/reso...interface.html

I routinely charge my 810 with a car charger: Radio Shack 273-1335 with output of 6 volts 500 mA. It's rated to work for 12 to 24 volts input.

Good luck

PS: I use it in an RV with the engine off if this is what you mean by static.