[brucepick]

True that you can hook both batteries in parallel to the charger.

But if you run them down low your overnight charge will only charge them up a small fraction of what they can hold. Beware. Beg, borrow or steal a charger rated at least 10A, and 20A or more would be nice.

Since you're using a 1.5A charger it will provide only about 0.75A to EACH battery and each will take approx forever to charge at that rate. A car battery of average size will hold something like 40-60 Amp Hours (40 amps current for an hour, or 1 amp for 40 hours, etc). So 1.5A of current trying to charge up approx 100AH total of battery capacity (if both are significantly low) would be about 65 hours of charging!

Sorry I don't recall how far you're driving daily. My Civic uses about 10A if not using fan or headlights. Headlights adds approx another 12 amps. So a one hour drive with headlights is about 22 amp hours. Two hours drive with headlights is approx 44 AH. After one hour's drive (22AH), if I recharge the battery with a 1.5A charger, would take 14.7 hours. So I use a 10A charger instead, and let it run on a timer at night.

Related:
Not ideal to run batteries in parallel.
If you read up on batteries on RV sites, you'll learn this.

What happens is that the battery with more charge will flow charge into the other one. That way they both end up with only a partial charge. And there are inefficiencies in that charge going back and forth between the batteries, so you always end up losing a certain amount of the charge you had.

Consider doing what I did, or a variation on it.
My front (starter) battery has the positive terminal wired only to the starter. That's all. My deep cycle battery positive terminal is wired to the main fuse box terminal that provides current to the rest of the car. I charge each battery separately so the charger knows when THAT battery is fully charged, and it goes into its "float" or "maintenance" mode.