my battery charger

I have an older NEWMAR HDM 50 3-bank battery charger...

I've been doing some "research" and I'm worried that leaving it on 24/7 isn't great for my batteries. When the batteries are full, I believe it constantly provides a small voltage to the batteries to keep them topped off.
It seems newer chargers are able to periodically check levels with a short charge--instead of constant.

Is my thinking close?

I have 3 DEKA 8D batteries (not AGM)

Constant float is fine for lead, as long as voltage within mfg specs

lowcountry, my IG has an even older Newmar, I`d bet both are original. I call mine the Jurrasic Mk1 prototype model. Both are old tech ferro resonant. The way I use my boat I`ve not bothered to update, esp. as I have a modest solar array. The charger is not connected when I leave the boat, solar keeps the batts full.
One thing I wondered,I hope john61ct will know this, is the 10amp output your charger shows total output, or 10A per bank? I`m guessing total.

I have that exact charger in my garage. I use it occasionally on cars, lawnmowers, etc.
It is the old "ferroresonant" type, and has only the same charging characteristics as a car alternator, unlike the modern 3 stage "smart" chargers.
However, that doesn't condemn it. Mine worked just fine for many years. I replaced it with a Xantrex Inverter/Charger in 2000, after 20 yrs of faithful service and no issues being connected to my batteries all of the time the boat was plugged into shore power.
I had a pair of 8D and another pair of 4D and a single 4D connected to its 3 output lines. None of those batteries suffered shortened life, I got 7 yrs lifetime out of all of them.
With the Xantrex operating on a "Smart" propocol, I have had 10 and 12 yrs from my batteries, but that is not the only change so I can't say the old charger wouldn't have done that well in the rest of my newer regime.
YMMV

NewMar has good customer service, even on old stuff (at least they did on the 30 year old items on my boat)contact them with any questions. https://dcpoweronboard.com/contact-us/

My boat has a Newmar 45 amp (in your dreams) two bank charger that is over 30 years old. Why do I keep it? It works!

I have a similar model but 20 (or 25 do not remember) amp max, it is working perfectly. Old but charging the batteries as expected. All mine are lead acid and for the last 2 years I have no issue with it. When batteries are fully charged it acts as a trickle charger.

L.

we have a similar battery charger, as a smart charger in the inverter. The ferroresonat charger is powered through a mechanical timer so it just runs 15 minutes a day. no cooked batteries.

Thanks for the reassurance! I'm just going to leave it on and not worry.

If it is a ferroresonant charger do not leave it on all the time.

I have an older promariner ferroresonant charger that killed two batteries when left on for a couple of months. Boiled them dry and cracked a battery case.

Easy enough to keep tabs on output voltage and amps for any charge source, never just take their word for things.

Even (especially) new out of the box they usually need adjustment to do the right thing as per bank's mfg specs.

Long as float voltage is properly low and the bank is sound should be no problem leaving it on 24x7.

It`s a comparison between the reliable old style ferro resonant and modern multistage chargers which may be less reliable or long lived, but more likely to get the batts full and hold them there without overcharge.
If I didn`t have some solar I`d update the old Newmar, though when I suggested updating to a shipwright, he said reliability might outweigh new developments(not in those words!). We see posts on TF about problems with modern chargers, but I think they have charging efficiency ferro chargers don`t.

"We see posts on TF about problems with modern chargers, but I think they have charging efficiency ferro chargers don`t."

One hassle with "modern" chargers comes from DC system use dockside.

Should say the DC fridge be on ,and the FW pump switch on the batt voltage can drop to the point where the charger will begin a charge cycle.

This will pump 14+ volts into the house untill the thing thinks the batt is back to 100% full and switches to float.

This causes a requirement for more frequent batt watering .

My 1985 Endeavour CC came with a Ferroresonant Charger. It was always on and at a constant voltage as long as it was connected to 110V AC. I also had a 12 Volt only refrigerator. Rolls Battery did not recommend continually charging their batteries and, if I did, the voltage should be around 13 Volts not 13.5 - 13.7 as is the normal range for lead acid batteries. The best chargers at the time were 3 stage chargers with the final stage in the 13.5 - 13.7 range.
After a great deal of research, I discovered Analytic Systems and purchased their BCA310-110-12 model. This is a 12 Volt 3 stage charger that also functions as a power supply. After returning from a trip, I would charge the batteries until the output current. with all DC loads off. was about 0.5 Amps. I would then turn the charger off, turn the battery switch from both to off and turn the charger back on. It now functioned as a power supply and I was able to run the refrigerator, lights, etc. without being concerned about overcharging the batteries. I called Analytic Systems today and they still make this model as well as newer chargers, some of which will also function as a power supply.
I have ordered a new trawler that comes with a Victron Inverter/Charger (with Storage Mode) and a refrigerator that will run on 12 Volts but switches to 110 V AC when available. I anticipate that this configuration will work great.