New to solar. questions on fuses, breakers, and grounding

[njp6x6]

Is there an issue connecting a 100 amp hour and an 80 amp hour battery in parallel ( if they are both in good condition)? I am starting with just one battery but looking ahead to the future. I am guessing I should not connect an old battery that has been cycled below 50 percent many times with a new battery

[SunEagle]

Is there an issue connecting a 100 amp hour and an 80 amp hour battery in parallel ( if they are both in good condition)? I am starting with just one battery but looking ahead to the future. I am guessing I should not connect an old battery that has been cycled below 50 percent many times with a new battery

Yes. If the batteries are not the same Ah rating and age then you will get unequal charging and discharging. That will kill the weakest battery first.

[njp6x6]

I have an 88 amp hour battery. If I wanted to connect another panel in the 30-50 watt range with the 100 watt that I already have and use my single battery would this be a problem?

[SunEagle]

I have an 88 amp hour battery. If I wanted to connect another panel in the 30-50 watt range with the 100 watt that I already have and use my single battery would this be a problem?

Again. Unless the panels Vmp & Imp are very close to one another you will not get them to work well together. Wiring them in parallel or in series will result in less than the total amp output.