Aux battery could mean anything dependant on application. If you want a deep cycle batt, go with what Ed says. back to your OP, no it does not matter if your aH ratings are a little out. I have been running 2 standard batteries for over 2 years now with no problems (Winch, fridge, lights, compressor, inverter etc.) one is IIRC 110aH and the other 85aH. both starter, not deep cycle batts.
onto your OP again, I would get a dedicated 12v laptop charger and NOT run it through your inverter. Your inverter (depending on Watt rating) will draw a massive current only to downsize it to <20v for your laptop. There is no need for this. you are wasting juice. work out why you really NEED the inverter then try to get those bits of kit down to 12v. I have a 300w inverter intalled and have yet to find a reason to use it. laptop runs off a dedicated 12v system and everything else works off 12v.
G
