Battery? Charger? Who's at fault.

[sailak]

My system:

2 Grp 27 lead acid batteries set up as 2 banks. Batteries are 5 years old. They are left in the boat for the winter with the charger hooked to shore power.

My shore power charger is a Professional Mariner Pro Mite 15/20. It looks to me like just a trickle charger.

The issue:

The batteries are only coming up to 12.5 to 12.6 volts even after extended time on the charger. They have in the past been over 13 volts. I checked the electrolyte, checks 1.275 or higher specific gravity. I cleaned the cable terminals yesterday, no difference noticed.

The charger never shows more than 2 or 3 amps when charging.

Should I take the batteries out and have them charged to see if they will take a charge?

Is the charger on the fritz? should I see more than 2 or 3 amps when charging? Now with the one battery down to 12.2 it's showing 2 amps. If I meters the leads from the charger what voltage should they show? I was getting 12.5 yesterday metering on the back of the switch where the charger wires connect.

Any help appreciated.

[mitiempo]

I tried to download the manual from Pro Mariner but couldn't. However it is described as a fully automatic charger. If it is charging the batteries it should measure about 13.2 to 13.5 volts if they are fully charged and on float. If they are not fully charged - and at 12.5 volts they are at about 50% - the charger should be between 13.8 and 14.2 volts. Not sure about your batteries health but the charger doesn't sound too good.

[sailak]

I'm wondering about the charger as well.

How can I test the charger?

[motion300]

I would turn the charger off , put a load on the batteries to drain them some then turn the charger back on and see what happens

[sailak]

Had both batteries down to 12.3v then back on the charger. Still only showing 2-3 amps.

I'm going to use a different charger and charge the batteries up full and see how they do after a good charge. I did about 40 minutes of charging with the engine (in gear, 2000RPM) and got them up to 12.7.

I'm starting to feel there may be a new charger and a couple of AGM batteries in my near future.

IF I go with AGM do I need to change anything on the alternator system?

[mitiempo]

You shouldn't have to change for AGM batteries. Their charge voltages are very close to flooded voltages. But AGM batteries are not the answer to everything. A change to AGM is usually best done along with a full rework of the alternator and/or regulator as it will have to work harder than ever. Good flooded golf cart batteries are still the best value and will not require any other changes. They regularly outlast AGM batteries as well.

You posted the charger was only outputting 2 - 3 amps - at what voltage? It does sound like both the charger and batteries are near the end of their usefulness.

[sailak]

Originally Posted by mitiempo

A change to AGM is usually best done along with a full rework of the alternator and/or regulator as it will have to work harder than ever.

Because of the AGMs? Why will they work harder?

Good flooded golf cart batteries are still the best value and will not require any other changes. They regularly outlast AGM batteries as well.

I don't have much room in my boat for a lot of batteries. The present battery area is just big enough for Grp 27 batteries -- it's only 9.5 inches in depth. I was thinking with AGMs I could go with Grp 31s and lay them on their sides.

You posted the charger was only outputting 2 - 3 amps - at what voltage? It does sound like both the charger and batteries are near the end of their usefulness.

That was at 12.5 volts.

[mitiempo]

Last first - the charger, regardless of the output amperage, should be charging at about 13.2 for a fully charged battery and over 14 volts if the battery is at 50%.

AGM batteries have a much larger acceptance rate than flooded batteries. A flooded battery of 100 AH, at 50% charge, will accept 25 amps charge until it reaches 80% charge. An AGM of the same 100 AH size at 50% will accept over 100 amps of current until it reaches 80% charge. Lifeline states up to 5 x capacity, or 500 amps. The charging system will work harder and as long as the batteries are under 80% charge the alternator can be at max output. For a small bank this is less of an issue but if the bank is larger in capacity the alternator will run at max output for longer than it is designed to.

For a bank of say, 300 AH from 50% charge to 80% charge is 90 AH. If the alternator is 55 amps it will run at max for over 1 1/2 hours. They are not designed to do this. The solution is an external regulator with an alternator temperature sensor. Ideally an external reg like the Balmar MC-614 is chosen which allows you to dial the alternator back from max output to help. An alternator rated at 100 amps running at 80% is better than an alternator rated at 80 amps running flat out, even with a temperature sensor.

Many alternators have been done in by AGM batteries.

I understand the situation of space - is there no other location for the batteries?

[sailak]

I was aware the AGMs could accept charge at a higher rate...didn't think about that working the charging system harder....duh!!

As for battery space....as always it's a compromise between stowage and stuff. There is room under the starboard settee for a couple of 27 or 31 sized batteries at the cost of some storage.

I quit my job, wife only working 3-4 days a month for the summer so we're going to be able to spend enough time aboard to figure out what we really need and what we can do without.

Thanks for the help!

[Stu Jackson]

Wait! A 36 foot boat and you can't find room for at least four batteries (3 house and a small reserve bank)???? Sounds like either it's an old warhorse racing boat or your storage space took over your electrical system! We have three 130 ah 12V wet cell batteries for our house bank on a 34 foot boat.

If you're doing anything other than marina hopping, you'll need more electrical storage capacity.