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Sterling Power 20 AMP charger with temp sensor - have I ruined my battery bank?

Feb 25, 2018
Sabre 30 None Long Island
I purchased a Sterling Power 20A charger from Maine Sail.

When I charge my 12v bank (brand new 2 x Interstate CG2) during this winter, it's putting in 15volts.... sometimes up to 15.3volts.

I'm guessing this is temperature adjusted because I connected the temp sensor to the batteries ?

Is this high voltage charging hurting my new battery bank?

Note: I have only had to charge 3 times at this 15.3voltage - a top up to full at the beginning of Winter. The bank sat at 12.73 for months, but it was at 12.70 yesterday when I visited the boat, and so it gave it a little top up and it occurred to me that 15.3volts is not good.

Jan 11, 2014
Sabre 362 113 Fair Haven, NY
Have you checked the charger's program to make sure it matches your battery type?
Feb 25, 2018
Sabre 30 None Long Island
Good point - Yes I double checked the program, I called Interstate and got the data sheet for my batteries. Not at the boat now, but I think I am using one of the Lead Acid presets.
Jul 7, 2004
Hunter 30T Cheney, KS
Defective charger maybe? Not sure if there is any way to know if they are damaged. Did they boil over?
Feb 25, 2018
Sabre 30 None Long Island
Uurgh I am just not having much luck with battery chargers.. I threw my previous charger out for over charging...garbage Schumacher "Marine" that would hit 16volts and probably ruined my previous bank....

This is a ProMariner ProNautic 20 Amp.
Thanks for the replies, no boiling or hissing. I made sure they were properly topped up with distilled water.
Yesterday when I put the charger on, it started out at 15.3v 17amps and quickly scaled down to 15.0v, the amps scaled way back and the charger shut off after about 1hr.
Oct 22, 2014
CAL 35 Cruiser Portland OR, moored EVERETT WA
More likely it is the Temp Sensor. When I installed mine I was seeing high charge voltage. @mainesail said to disconnect the temp sensor at the charger, till summer. It sees the batteries as "cold" and so has no worry of too much charging.

Make sure you have adequate water in the batteries.

You can check the batteries by using a Hydrometer or a Refractometer.

They will give you a state of charge based on your electrolyte.

Be sure you have the charger set for Open Lead Acid or Sealed Lead Acid setting.
Feb 6, 1998
Canadian Sailcraft 36T Casco Bay, ME
I purchased a Sterling Power 20A charger from Maine Sail.

This is a ProMariner ProNautic 20 Amp.
We don't sell the ProMariner chargers, although we certainly can. We choose to sell only Sterling Power as they represent a better value. A charging voltage of 15.3V may be 100% normal, depending upon battery temperature. In cold temps charge voltage is compensated up and in warm temps it is compensated down. If the batteries were cold 15.3V is not out of the question at all.
Feb 25, 2018
Sabre 30 None Long Island
Hi Maine, and everyone,

Yep - I looked up my receipt, it's a Sterling ProCharge Ultra.
Paypal - Transaction ID: 80G32013Y1767072E / Mar 11, 2018 18:57:09

Thanks for the responses. I feel a little better knowing it could be normal, the boat is on the hard in the Port Washington area, and so it's possible that cold temps could have made the charger compensate.

Should I continue to use this charger during winter layup with the temp sensor attached to the batteries, or is it safer/better to detach the temp sensor during winter layup charging?

Well, actually how much more winter do we have left anyway... soon we will all be back in the water :)

Thanks again for all the help, what a great forum
Feb 6, 1998
Canadian Sailcraft 36T Casco Bay, ME
I am not a fan of:

#1 Unattended charging and most boat yards actually disallow this practice.

#2 Leaving the temp sensor plugged in all winter, if you doing are unattended charging.

In the winter I simply unplug the temp sensor from the charger but leave it connected to the neg terminal of the battery. In the spring/summer jut plug it back in..

If you are just doing short stints of "opportunity charging" eg: when you visit the boat the temp compensation is fine..
Feb 25, 2018
Sabre 30 None Long Island
Thanks Maine Sail,
Yes good point to make - I am strict about only charging batteries while actually being ON my boat, I don't like to wander around the boat yard while my batteries are charging. I don't ever leave my shore power connections or extension cords connected when my boat is unattended.
Actually to be honest, boat yards should enforce this more, I see too many boats in our yard plugged into overloaded electrical outlets ALL winter, zip tied cords to the power outlet stands along with 5 other boats... with a zip lock plastic bag covering the outlet.... sigh.

Same as the guys who hoist their sails while on stands in the yard... next to a row of other poor unsuspecting boats... just one puff of wind and it's domino time...

The halyard slapping owners causing the boatyard winter symphony...

But I've digressed :)

Thanks !
Nov 16, 2012
Catalina 310, 2000, #31 Santa Cruz
I had a problem with the temp sensor cable on mine. I used an RJ-11 (?) connector to get it to reach the charger. It had a flakey connection so it thought the temperature was much lower than it really was and set the voltage too high. Replaced it with soldered connection, no problems now.
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Nov 14, 2016
Hunter 386 QCYC
Hey guys. Apparently ignorance here (Toronto), where I see, and practice, the newly learned "don't charge the batteries when not on boat rule". Most everybody I see at two different Marina's over the course of owning this boat over the past 3 years leaves their battery charging during the week. Seriously, is this bad practice? The downside struck me as if the battery drains (old boat, weird stuff), I don't have a working sump pump. Thoughts?
Jan 11, 2014
Sabre 362 113 Fair Haven, NY
We leave the boat plugged into shore power during the week. Primarily to keep the refrigeration running. Since we spend most weekends on the boat we leave some food and condiments on board so we're not schlepping it back and forth. That and having a cold beer when we get there.

If we had an older less reliable charger or did not have refrigeration, then we might leave the boat unplugged while gone.
  • Helpful
Likes: Ward H


Apr 27, 2016
Catalina 320 Holland, MI
I experienced this same high voltage charge thing with my Promariner Pronautic 40 amp smart charger (Model 1240P ) the first Fall after putting my boat on the hard for the winter. So, I emailed the manufacturer saying "Even though seemingly fully charged already, I just recharged my sailboat batteries (two Deka 904Ds) after having them disconnected from shore power for about a month. I did this to top off the charge after the boat had been hauled out of the water for the winter. My charger is set on the preset 2 profile for flooded batteries. Everything seemed fine (all LEDs read correctly) except that the charger put out 15.1 volts conditioning DC for about an hour (with rapidly diminishing amps). Then the charger went straight into standby. I'm concerned why the charger put out 15.1 volts in the preset 2 flooded batteries mode? According to my manual, it seems like it should not do that in my selected preset mode. I never saw it do that all summer (maximum was 14.7 volts conditioning)"

I received this reply from Promariner:
" The output of the charger is temperature regulated. Depending on the ambient temperature the charger will increase the voltage to compensate for cold batteries and decrease the voltage in hot temperatures.
ProMariner Support

I have topped off my batteries since this first experience in cold weather, in the same manner with the same results (High voltage with high initial amp output diminishing very rapidly) with no apparent detrimental impact on my batteries. The charger does this for one hour and then puts itself into standby. I have always stayed with the boat or come back very soon to shut off all power to the boat.