Amp goes into protect mode at 4 ohm but not 1 ohm

After I rewired my subs, two 3002d4, from 1 ohm to 4 ohm, the amp began going to protect mode at high volume levels. I wired them to 4 ohm because the subs would get a little smelly and I didn't want to blow the subs. I checked all my wiring and it seems to be fine. I checked the batteries and I noticed that they aren't identical either. It had two batteries in it when I bought it. Battery number 1 is duralast gold with 1000ca and battery number 2 is a Napa 1040ca. There in wired + to+ and - to -. I have a 100 amp fuse between the second battery and the amp. The fuse is so low because I haven't done the big three yet and I'm afraid of burning he wires up. Any help would be nice. I've only blown one 100 amp fuse using a Brutus 2400.1 that just doesn't sound right to me

+ to + and - to - is parallel.

To clarify I was speaking of the batteries and I thought that was the proper term I was just unsure. Is it OK that they are not identical

fuse is too small for that amp, it needs to be a 250a and you are setting the gain too high

I know the fuse is too small. The point is to avoid stressing the wires under the hood until theamp weather permits me to do the big 3. I'll look into the gains but I never changed the gains from when I had it 1 ohm

It's not an issue with your fuse. Sounds like the subs are not wired properly. Did you check resistance with a multimeter?

I'm not sure exactly what it was but I'm leaning towards gain matching. I took the subs out, replaced all the wires and took some time to tune the amp. I also replaced the fuse with 200 amp one. And I'd also like to know if the battery's not being exact matches is OK.