The Offshore Voyaging Reference Site

Sneaky Power Users

We were on the boat for a couple of days last weekend and one evening I decided to check email and the weather on my iPad.

But when I picked it up, it turned out I had forgotten to charge it—it was as dead as John Cleese’s parrot.

Not a problem, we have a USB charging port on the boat and a USB C (it’s a newish iPad) cable.

I plugged in the iPad and, since this had reminded me, my iPhone 13, then at about 50% charge, into a different port.

The photo at the top of the Tip shows the total current draw before plugging in these devices:

  • Five LED lights on below,
  • AIS with drag alarm,
  • propane sniffer,
  • boat monitoring system,
  • and two anchor lights
    • will be another Tip and is why the radar is on (in standby).

The photo below shows current with both devices charging, and no other changes.

Yikes, these two handheld devices are drawing 3.5 amps at 12 volts, or 160% of what it takes to power a small boat at anchor at night.

Yes, I know, in a couple of hours or so both devices will be fully charged and only require a trickle of amps to keep them there.

Still, suppose Phyllis charged her iPad and iPhone, too, and then maybe we have guests with devices, and then there’s the iPad we use for navigation. And many boats have one or two laptops…

It’s stuff like this, albeit not by itself, but added to other sneaky users of amps, that push cruisers into expensive electrical system upgrades including: excessive arrays of solar panels and/or the clutter, noise, and weight of wind turbines; or a generator.

Worth thinking about.

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Michael Jack

That explains a lot, John. This summer, I was on the boat by myself for a bit with a Samsung Galaxy Tab and a Samsung phone. The boat batteries managed fine. Then my wife arrived with an iPhone and a Mac. The batteries already started to empty surprisingly fast. Then my two daughters arrived with just their iPhones and that put things over the top. I really have to figure out this winter how to generate more electricity (or have less visitors but that won’t happen :-))

David Eberhard


Great points about easy to overlook loads.

Years ago when I purchased a new Paneltronics dc load center, I opted for the new whiz bang led digital meters and led pilot lights showing what circuits were energized. Oh it all looked great. It wasn’t long before I realized that I was losing a good 4 amp hours every day! I added a simple switch to what powered the meters so I could turn them on when I wanted to check things. All others times, they were off. That made a great difference. The next thing I looked into was all of the led pilot lights that were always on. Things like cabin lights, bilge switches, anything else that was normally always on. I just removed the wires that were powering the lights. That also lowered the energy consumption some, but not as much as the panel meters. There was the unattended bonus that it was very easy to see if something was left on that shouldn’t be. Normally there are no pilot lights on.

Darren Greenhalgh

i was having the same issues with my 400amp/hour lithium battery bank. when the kids were on the boat playing board / card games all night then wanting to charge their phones i noticed that the battery was significantly low – especially in the winter months here in the pacific NW. so, instead of growing my battery bank i just bought 2 small jackery battery/inverters for the boat so the kids can use them to light the LED lights i installed and also charge their phones at night. one in the main cabin and one in the aft cabin. i just charge them either on shore power or when the engine is running. they work great and was a simple solution to my battery needs and less work than jumping into the main lithium battery bank. there is a down side to them though – more crap on the boat. i have a hard rule now – i cant bring anything else on the boat unless i take something off of the boat with comparable weight!!!!
im not sure if there are any other down sides to my knee jerk reaction of supplementing the battery bank with the jackery portables.
can you think of any?
john, this is THE best site on the internet for cruising information – a huge thank you your way for all of the time you have dedicated to the site – love it!!!!