Flat battery/Solar powered trickle charger for AMV8?

I recently returned from holiday (after just over two weeks) to find the battery in my AMV8 completely flat. A couple of other Vantage owners have said to me that it's quite a common problem with a Vantage and so I should buy a trickle charger. This poses two questions:

[1] Should I be concerned about problems with the electrics? The AA came and checked the car and told me that the battery is in perfectly good nick and the alternator charges it fine, but there is a fairly high drain on the battery when the ignition is off - is this normal?

[2] My car is parked on the street and so I cannnot easily plug in a trickle charger. Someone suggested to me that I could look at a solar powered trickle charger instead (to plug in through the cigarette lighter), but I'm worried whether that safe/good for the battery?

Any thoughts would be significantly appreciated!

Thanks,
Andy