Boiling Batteries

I have a ProMariner 5/5/5 on-board charger mounted in my 1996 Ranger R70 Sport. I cannot keep water in the (2) trolling motor batteries. I am supposed to be able to keep the battery charger plugged in all the time, to "condition" the batteries, but cannot due to the batteries boiling. Is it likely I have a bad cherger? Who out there can recommend an affordable (under $150) on-board charger that doesn't boil the batteries?

Re: Boiling Batteries

bad charger, it should shut down when fully charged, then trickle. there are so many to choose from.

Re: Boiling Batteries

Since this is a three output unit but it only boils the troller batteries, I suggest you disconnect all of the outputs from their respective batteries. Connect the output for the start battery to one of the troller batteries. If it still boils, move it to the other troller battery. If that one also boils but that output does not bother the start battery, I'd say you have a couple of bad troller batteries. However, before doing anything, connect one of the troller outputs from the charger to the start battery. If it boils, that points to the charger. Repeat the test for the other charger output. So you could have an either, or, or both situation. Bad batteries and a bad charger that killed them. That charger should not boil the batteries. You could also stick a voltmeter on the battery being charged to see what the charge voltage actually is. Lastly, if this is a charger that "load shares", I would then almost suspect that the load share circuitry has gone south.

Re: Boiling Batteries

Thanks, Silvertip. I like the process of elimination idea. I'll try it. The batteries all show around 12.4V while disconnected. If I connect a voltmeter to the battery while charging, will this be an accurate charger output reading?

Re: Boiling Batteries

rhgoudeau said:

Thanks, Silvertip. I like the process of elimination idea. I'll try it. The batteries all show around 12.4V while disconnected. If I connect a voltmeter to the battery while charging, will this be an accurate charger output reading?

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Not exactly, the current drawn by the battery will pull it down some. But if it reads over 15v it will be a good indication that the charger sensing has gone south. Too high voltage will cause higher current (Ohm's law) and also heat, initiating boiling.

Re: Boiling Batteries

I agree with Wire 2 but suggest the finall voltage should be in the 14.4 to 14.8 volts range.

Also how are the trolling batteries connected?

Can your charger charge a 24 volt trolling battery when batteries are in serries?

Re: Boiling Batteries

With a voltmeter connected, I get 14.5V+/- at each battery while charging. The troller batteries are set up for 24V operation, the charger is made for this setup. It's looking like I have two bad batteries (bad cells in each, according to a hydrometer). I guess I'll get two new batteries, and try charging them with the onboard charger (keeping a close eye on the water levels). At the slightest hint of boiling, I'll be looking for a new charger. BTW, I connected a portable charger to each troller battery, and almost immediately saw bubbling in the battery cells. Is this any indication?

Re: Boiling Batteries

As a final check, have them load tested at any auto store but in my view, you have two junk batteries.

Re: Boiling Batteries

If the hydrometer shows a difference from cell to cell, the battery is done. That will cause uneven voltage distribution on the 6 cells in series.
e.g., 1 cell may drop 1 volt, the one next to it makes it up with 3 volts. The 3 volt cell will boil very quickly.

Re: Boiling Batteries

So, how fast will a bad charger trash two new batteries? I plan on getting two new troller batteries (the hydrometer shows the cranking battery is O.K.), but I still don't trust the charger.

Re: Boiling Batteries

There are a number of factors that enter into that scenario. The first we already touched on. Some multi-bank chargers do load sharing which means each output is totally separate and dedicated to the battery to which it is connected. However, when that battery reaches its fully charged state, that output is connected to another output to help it with its duties. So if the load sharing circuitry goes bad, the normal output can be forced high during the load sharing sequence and therefore boil the battery. How long that takes depends on how high the voltage goes and how hard the battery boils. Then there is the situation where the regulation circuitry on one of the outputs goes bad and fails to regulate at all. So now both batteries get boiled. You know the batteries are bad so replace them. when you connect the charger, montior the voltage and the batteries for an hour or so. voltage should stay in the specified range (about 14 - 14.5V) and the batteries should not boil.

Re: Boiling Batteries

Tasha's daddy hit the nail on the head. I wouldn't even mess with it. If it doesn't work, that's it. The cost of a single battery can be what a really good digital peak charger would cost.

I have the Black and Decker ones with adjustable charge rate, desulphate, battery diagnostics and auto peak and trickle. Cost? 40 bucks at Wally World. A nicer one is about 60. We have 3. They all work great. Would never settle for anything less now. You can just set it to a very low setting (even 2 amps for a huge marine deep cycle) and then put the boat in the lift and go to bed. When you get up in the morning the display will say FUL (only 3 digits available on my model) and you unplug it. How easy is that?