Solar batteries. North Star

[Durian Fiend]

Yes, you should remove the bad batteries because if left in the array their presence will weaken the good ones. 
What do you use at night that creates such a high demand?  If you could do your high energy work during the day when solar is working for you that would be ideal.  The 5 batteries may not last much longer in any case if they are heavily taxed on an even greater basis now with less storage capacity.

Regarding the warranty, I'm afraid you will need to go straight to the manufacturer source for relief.  At least that's my experience with  inverter and charge controller issues purchased locally from Ultimate Off grid solar.  Batteries could be different since they're not something that's easily shipped.  Check with your installer.

  My overnight demand is primarily a large modern energy efficient refrigerator / freezer , a Tv and satilite, plus wireless router.  Yesterday i put the refer on a timer to reduce the load overnight.  I only run other high wattage things during mid morning.   My solar panels send 92 in ,  from 8 400 watt panels and by the late afternoon, the out is around  57, by sunrise its been around 48/49   The batteries are in absorb stage by early afternoon.

Yeah, that's not such a large demand.  How many Amp hours are the batteries?  I have less panels than you, only 5 for about 1800 watts, and have similar loads.  Smallish TV and efficient 12 volt fridge must be the difference.    My two batteries are in absorb stage by mid morning.