A Battery of Confessions form an Unconventional Electron Pusher (and Puller)

Big Duck has 4 batteries, no two the same. We have a flooded 24 and a flooded 27 for house and start, but I don’t really know which is which. 

24 and 27 under the green hose

I have a group 31 AGM for the inverter 

Group 31 on the Port side.

and a small lawn mower battery that displaced the tiny starting AGM for the EU3000i Honda Generator.

Lawn mower battery under a flybridge seat

 How do I keep them ‘up’?

I know there are sophisticated systems, but I’m a lazy, casual SOB so I just use what's there, then add on stuff until I’m happy with performance. This means I’ve got 3 different battery ‘feeders’ and two battery combiners. I’ve also got a timer and of course the usual 1, 2, both, off, battery switch (which I seldom touch). I’ve also installed digital voltmeters for each battery – these voltmeters do draw power but because my boat is on shore power in the back yard I just leave them on all the time.

The boat came with a 10-amp dual bank charger for the starting and deep cycle house batteries. 

On board charger with red light showing when charger is feeding the batteries - it's off when fully charged.

This is a very nice unit and as has been suggested for optimum performance, it charges the batteries and maintains them, shutting itself off when the batteries are fully charged. This unit keeps the fully charged batteries at about 13.3 volts according to my voltmeters.

So then I put in an inverter/charger – a Freedom 30, using a group 31 AGM to power the inverter so I could keep my 120vac fridge and freezer running while underway; 

this worked fine except for extended road trips when we didn’t need the boat generator for a/c or heat overnight. The fridge and freezer would deplete the 31 about the 3^rd day unless we ran the boat generator.

I tried running a lead from the van’s breakaway battery charging circuit to the AGM but it never proved itself – we’d just run the generator at night in the Walmart lot and have the inverter/charger pump amps back into the 31.

To simplify things while in the water, I decided to make the boat alternator charge the 31 by using a VSR (voltage sensing relay) to combine the house (or starting) battery with the 31 while the boat was running. While I was at it I installed another VSR between the house and starting batteries. Now whenever there was a charging voltage, all 3 batteries would be combined. This also allowed me to force a combine of all the batteries on the road so I didn’t have to worry about depleting the 31 and ‘starving’ the fridge and freezer of power on longer road trips if we didn't run the Honda while overnighting.

The ‘forced combine’ did prove to be a little inconvenient when it ran down all 3 batteries and I couldn’t start my boat at the ramp, but firing up the generator and having the inverter/charger feed 140 amps let me start the mill immediately.

In summary, all 3 batteries would now be charged whether on shore, generator or ships power... and I’m happy -- even knowing that batteries of different sizes, ages or types need their own separate sophisticated chargers. My goal is not to join the fight to keep a battery going as long as possible but rather to replace a cheap battery at the first sign of trouble. Also, I never have to mess with the 1, 2, on, off switch – ever.

So how do I know if/when battery trouble is lurking?

Maybe once a year or if there’s a hint of trouble, I’ll turn off external power and light up a 1,500-watt heater using the inverter. I’ll run the heater for 15 or 20 minutes – the gauge showing 100 12-volt battery amps being used to power the heater. 

Using 100 12vdc amps to power the 1,500 watt heater

I guess this isn’t a big load considering there are 3 batteries providing power, but it’s good enough for me to watch the voltage of each battery when the heater is turned off. If they’re all pretty close I’m happy. If not, I drag $100 out of the wallet and bring in a new 3-year car battery from Walmart.

Then, because the on board charger keeps the batteries at about 13.3, while the inverter/charger ‘maintains’ at 14.4, I turn off the inverter charger and let the on board charger manage the batteries for extended periods in the back yard.

I’ve only talked about two of the three battery ‘feeders’. I guess I call them feeders because there so much talk about bulk, absorption and float charges that I can’t keep all that technical mumbo jumbo stuff straight. But I do think that storing a battery at 13 volts is better than at 14 volts, that’s why I use the on board charger instead of the ($1,200) inverter/charger.

The fourth Big Duck battery is a lawn mower battery to start the Honda generator. The little Honda OEM AGM battery needed to be replaced every 18 months so I decided to wire in a (remote) lawn mower battery instead of having to dismantle the generator to change the little AGM.

The EU3000i generator has a remote (key fob) start so there’s a small draw from the generator start battery when the key is in the “on” position. I guess I could turn the key to “off” but I’m too lazy. Instead I have a ‘feeder’ for the generator lawn mower battery. The ‘feeder’ is a Harbor Fright $9 ‘float charger’. One day I may hook it up directly to see what it does to the lawn mower battery, but in the mean time I use a timer so the ‘float charger’ only sees the battery for 15 minutes every 24 hours. This gives me a reading of 12.4 volts on the generator lawn mower voltmeter.

I don't track the time the batteries last, but I'm guessing I'm going on more than three+ years. And I'm certainly not knocking the folks who want to do it right, rather perhaps just wanting to encourage bottom feeders like myself to not be afraid of doing it their own way.

More on my battery philosophy here.