Is my Newmar charging cooking batteries?

What do you consider cooking? Flooded batter gassing off?
What are the voltage levels from a reliable DVM at the battery? Bank config?
Cooking flooded or another type of battery?
Charger set up correctly?
Not so old batteries?

Pumping in the amps near sounds like still a bad battery or something else is really drawing the current. Turn off or remove all sources of drain. Solor or wind regulators disconnected?

I'd be very careful ......a properly functioned charger should not cause xs gassing, certainly not boiling, nor heating of the battery.

Sounds to me that you are already cooking those new batteries.

A good properly functioning, modern charger will charge in a sequence which gradually reduces the charge rate until when full, it will start to cycle, while doing so it will maintain a full charge without harm

To me the disturbing part is not figuring out the cause the first time. If it was the charger, then I would not trust a rebuild of that same charger. However, it might be something else entirely and the charger also damaged. Unless something is addressed and fixed, it will happen a third time.

DVM's and Chocolate Tea Pots have a lot in common when it comes to DC Voltages.

Are there Battery Isolators in the system? They can effectively keep the charger from "seeing" the finished voltage, causing them to continue charging.

Dyring your test run tiday, would it be possible to take the fully you charged batteries out of the circuit? I'm afraid you will cook them if you continue to overcharge them.
I assume you are just running the the charger and not the ships engines.
Let's face it, you are proving much by destroying your batteries, and bad batteryou or cell will cause damage by overcharging good batteries.

I am still concerned that you may permanently damage your batteries, particularly the two that appear fully charged.
When you do your checks tomorrow, could you take those two out of the circuit....I cannot see the point of over charging them further.

If you do not have one, i would get a hydrometer, to check the specific gravity of the acid. This is the only reliable way to check a batteries state of charge, usually they come with details relating the SG to their temperature, thus a thermometer is useful too.

I would not trust your older charger, even if it has been repaired, as I mentioned modern chargers are more efficient and their computerized charging sequence is less harmful.

PS....I would not run the main engine(s) with the new alternator or the Genny at the same time. Just confuses the issue.

Run one at a time to eliminate the culprit.

Best of luck, batteries are too expensive to right off so fast.

It looks to me like you're just costing yourself more and more problems and expense. I would suggest a good marine electrician as the next step. I wouldn't qualify it to "independent" as I'd simply want the best I could find. As part of that you could get an estimate on the cost of converting to 24V as well as his recommendations.

Converting to 24Vdc will not fix your inverter problem.

You have a more scary problem; You have a wire problem that is not safe.
You are not sure where or what it is.
Most fires on a boat start from an electrical issue.

Is the security and safety of your friends and family more important than getting a proper electrician in there to ensure everybody is vertical the next morning???

You have a similar problem as myself, a 35 year old boat with masses of redundant wiring......l, i am presently pulling the redundant stuff out...there are miles of wire,..... hundreds of wire ties and other junk.

To be frank, it would cost a fortune to have her professionally rewired.

Nevertheless, in your case I would be very worried about cooking your new batteries.

Your old charger is defective, the fact it has now burned itself up proves it.

My old Huckins had 5 8 VDC batteries giving a total voltaget of 30VDC it worked quite well, but I changed it to 6 6VDC which provided 36 volts I thought it worked better.

If you are considering changing to 24 VDC, now is the time to do it.....buy a quality 24 VDC charger which will charge the same number of banks you have......wire it direct to the batteries and use a separate 110 vac cable to drive the charger. In other words you are not using any of the boats old wiring.

It should work......at this stage I would not wire the batteries to the engines alternators......if your generator is running your batteries will be charged.

My Huckins came with no alternators, I ran her without problem for some 20 years using the battery charger and generator only.

The KISS technology is often better......Keep It Simple Stupid......

At least this will get you on the water......you can look at revamping your wiring during the winter.

Best of luck.......drop me an email.....and we can compare notes.

You d be amazed at what some professional do... A few backs I helped a guy I knew brought his 90s vintage Viking 70ish to the abacos. He just an jnveryer installed by an electrician working at a reputable yard. It was a disaster waiting to happen with undersized wiring, no safety against backfeeding and more. Including installing it on a shelf almost resting on top of the generator! Nice and warm.