... The battery is flat again it wont take a charge any more...
For safety reasons, many smart chargers wont charge batteries below a specific voltage. My CTEK MSX5 smart charger is better than some as it only requires 2V before it will allow charging of a 12V battery while my 40 year old dumb as door knob charger will push volts into a battery at 0V
So, just take note that
if the battery wont charge when removed from the vehicle, it could be that your battery voltage is too low for a smart charger you are using. If that's the case, remove the battery from the car and use an older style dumb as door knob battery charger to give it a little juice (but dont leave it alone to charge, supervise it). Then when (if) it gets some volts into it, disconnect the dumb charger and connect a smart charger to fully juice it up.
If a dumb charger wont juice the battery, it's likely there is a short within the battery cause even a badly sulphated battery will show that its charging somewhat but quickly die when the charger is disconnected. Guess what i'm saying is that
wont charge and
wont hold charge are somewhat different but related things
Whatever the case, the reason for a dead battery needs investigation using a methodical process of elimination as FU manchu states. Anything less may just turn out to be throwing batteries at a problem that lies elsewhere. It may not solve the root cause if the vehicle electrical system is at fault and will simply cost $$ and you'll have the same issue return. Check the vehicles charging system really well and methodically check the electrical system for parasitic loss so you can identify any problem circuit.
If the vehicle is working electrical as intended and you do long trips each day, short trips may not really recharge the energy lost in cranking, then try your luck with warranty replacement as a battery should really last longer than 12 months.
I'd especially go the warranty route if it was the dealer that just did a software flash and they were the ones that sold you the battery earlier. That's because that mob failed to identify the problem as they should have done a more detailed check of the whole electrical system. Allowing the battery O/C voltage to drop below 12.2 volts will result in sulphation process occuring - allow it to occur frequently and it kills batteries - the dealer should know better than to think just doing a flash will fix a sulphated battery due to high parasitic loss
