Wednesday, March 4, 2020

Time for New Batteries - Again

Replacing our Sailboat's Batteries

Duracell 6v Batteries
April 2016
Our boat batteries are now 4 years old, they are showing their age and we're planning on some trips that demand we have confidence in our Battery System. We installed the new batteries in April 2016, just about 4 years ago, and in Florida that's not too bad. Then, I installed Duracell Batteries, but this time they will be Trogan 6v TROJT-105 Batteries and the best price I found is at Batteries Plus.

By ordering them online, they should be 10% off their already good price. But I'll check with the store to make sure that their In-Store price is the same as their online price.

I placed the order and they should arrive Friday this week. So we'll go down to the boat tomorrow (Wednesday) and remove the four old batteries.

The new Batteries have a 20hour 225ah capacity. At night, our Fridge/Freezer draws about 4.5amps, so that would be about 4.5*20 or 90ah if the fridge ran continuously, it does not! Our, very rough, typical night time usage includes:




DeviceAmps drawAHoursSub TotalsTotal
Fridge4.5125454
Anchor Light0.512660
TV441676
VHF Radio tx.51581
VHF Radio rx.21224105
Running Lights11212117



With 4 225ah batteries, 2 in parallel and those in series to provide 12v, we should have 450ah total.

If we consume about 120Ah per night, we should only drain the batteries down by about 25% (roughly) and that's our goal, to not drain below 50%.

Our Solar System pumps in as much as 8*350watts during the day.

So, if we're using 120Ah per day, we should have plenty to spare.

I'll have to work on the formula's for these calculations.

Oh! and if we run the engine, that can pump as much as 100ah per hour, but it's normally toned down to about 60amps per hour in bulk and quickly drops to 10/13ah in accept.


All of these figures are guesses, and when looking at good battery management, the % of discharge and rate of charge are so complex that I really think it's best to leave it to the battery management system and ensure that the data fed to it is as good as it can be. So I'm updating our alternator regulator so that it's part of the BMS rather then the islolated external regulator currently (pun intended) in use.

I'll post more realistic data when I have it. Meanwhile, it's time to pull the old batteries, so that's Wednesday's task. That and wire in the smart regulator.


The Battery Bay is located just forward of the Galley under the Cabin seat, which, on Eximius, is the original seat located beneath the current seat. Confused? I'll add a pic later.

The 4 Batteries are held very securely.
The wooden beam is bolted to a Fore/Aft beam which in turn is bolted to Vertical End beams inside the Battery Bay.














The new batteries fit like a glove. The Terminal positions are just slightly different from the old Duracell's but actually work out better.

The Trojans have a single piece cover for the filling ports. The slight difference in the terminal positions result in the covers being easy to lift off (the old Duracell fill covers required a twist action to unlock them)

The process to install them is:

  1. Place #1 as far forward and near to the midships end of the Battery Bay.
  2. Place #2 as far aft and near to the midships end of the Battery Bay
  3. Place #4 as far aft and outboard of the battery bay
  4. Place #3 as far forward and outboard of the battery bay
  5. Move #2 to touch #4
  6. Move #1 to touch #3
  7. Install the Forward Inboard Vertical location bar (3 screws and nuts)
  8. Install the central hold down beam and support beam.
  9. Connect the Battery Cables.



The resulting installation is complete. Now to test everything.

Solar Panels are still turned off (covers in place)
12.4v shows on the Battery voltage digital display (low, they need charging) They should show 12.6v when fully charged.

Turn Solar panels on (remove covers) and leave for 24 hours.

Voltage now 12.6v when panels are turned off and all systems are off.

Initial Fluid top up - filled each cell till dielectric can be seen touching the lower edge of the filler ports.

24hours later, voltage steady, solar panels output reduced to float stage.



Test engine start, all fine. 48 hours, relaxed each of the terminal nuts and re-tightened just to make sure cable stress is released.

The central hold down beam is not the prettiest, but those batteries are not going to move even if the worst ever happens.

Ready for the club raft up this weekend.

See you on the water.









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