Heyho!
So i had a walk in the outside about 2 hours. The old battery finished after 15mins, i added a fresh 9V block and the data was appended as it should. There were much less errors in the checksums as the first time. I think the 3.3V regulator was the right decision to add to the circuit. The leds blink much more the same tact. To be on the safe side i would say add a low drop regulator, maybe another card takes more current so you would need it anyways. And it´s only the cost of 0.75?.
I also made some measurement:
I measured with an 1R in series with the arduino and got
150mA at work. (140mA-175mA) at logging after init sequence, depending on write frequency (has to be analysed why sometimes more to write)
180mA at init sequence
25mA Arduino alone
78mA " & MAX232
80mA " " & LED stuff
140mA " " " without card
so the nice thing is, that sd-card writing is not current hungry! Gps is.
But you should have a big buffer, would be interesting to see with a good measurent equipment how the card behaves. I think there may be really short big peaks of current. An sd-card has a minimum maxWrite frequency of 25MHz per datasheet. Too short for me to see.
But when i look at it with my scope when i put the card into the slot without gps, i see that the card has it´s own logic. ca. every second it makes pulses about 50mA, so it may try to communicate or whatever.
That may not be super correct measured, but the whole measurement should be proportional right.
Same 1R, same fresh 4R25 6V battery.
That´s it about the electrical stuff. Hope that helps anyone.