Maintaining boat batteries.

[CanuckShooter]

I am new to this bigger boat business, my boat has 2 12v batteries one runs the sonar and is hooked to the main motor. The other is wired into the downriggers only.

What is the best way to keep the batteries charged up? The one on the main can get a charge when running the 60hp, but not the other one?

If they are put on battery chargers before going fishing, how long will the battery last running downriggers?

[elkhunter11]

How long the battery will last operating downriggers depends on the battery, and the downriggers. An AGM deep cycle battery will last the longest, and charge the quickest for the downriggers. I leave a battery tender on the battery, whenever my boat is sitting unused in the garage, which prolongs service life.

[Buckhead]

I use a Minnkota onboard battery charger wired from the main motor and also to the additional batterie(S). Once the motor battery is charged up then it switches over to the other batteries, so whenever the main engine runs the batteries are getting some charge.

[-JR-]

i would be switching your down riggers to your engine battery since you will be using your main engine for trolling or do you have a kicker for that. Maybe its got a charge out let to charge your down rigger battery .

[Coiloil37]

There are many ways to skin this cat and many ways to do it wrong. If you’re going to have a two bank system I suggest doing a little reading and doing it right. Being in fresh water on day trips you’re less likely to have serious problems like discussed in these articles but that doesn’t mean you couldn’t have trouble if it’s wired wrong.

I did a lot of additional reading before I rewired my boat but these should have enough info to explain what you need to do.

https://newboatbuilders.com/pages/electricity13.html

https://www.bristol27.com/projects/b...ounding-system


https://continuouswave.com/forum/viewtopic.php?t=4329


I suspect that’s overkill for the application but again, many ways to do it and very few are correct. If you’re inclined to know the risk and spend a little time reading you can start to see how it should be done. Then if you’re further interested you can read about specifics. Heck, a book can be written on properly crimping connectors and why they’re not soldered. Here’s one example.



https://marinehowto.com/marine-wire-termination/

Originally Posted by elkhunter11

How long the battery will last operating downriggers depends on the battery, and the downriggers. An AGM deep cycle battery will last the longest, and charge the quickest for the downriggers.

Elk it’s 2024. We’ve got lithiums now.

[Duramaximos]

I chose to keep two isolated systems for safety and redundancy.

Main motor charges 1 12v and runs the helm electronics.

Kicker motor charges a separate 12v and runs the down riggers and water pumps.

Sent from my SM-G990W using Tapatalk

[EZM]

I also run on board charger(s) - that the best way to keep batteries charged and maintained.

If your budget allows for it, it's a very convenient and effective way charging and storing your batteries. The pain of unhooking batteries, putting them on a manual charger, etc... etc... sucks. It sucks worse late at night or when it raining out too - so using one plug (like your car's block heater) which takes a few seconds is awesome.

I also run isolated and have the 24 volt ( 2x12v in series for 24v electric trolling motors ) and the 12 volt ( 2x12v in parallel for 150hp main engine, 9.9 kicker gas trolling motor, downriggers and electronics).

Whenever I'm parked, and have access to an outlet, the onboard chargers are plugged in. Batteries will last a long time if they are maintained. I am 13+ years on one set of 2 (for electric trolling motor), and just replaced the other set of 2 (for main engine, etc...) but just out of precaution (they were 11 years old and still good).

[elkhunter11]

Originally Posted by Coiloil37

There are many ways to skin this cat and many ways to do it wrong. If you’re going to have a two bank system I suggest doing a little reading and doing it right. Being in fresh water on day trips you’re less likely to have serious problems like discussed in these articles but that doesn’t mean you couldn’t have trouble if it’s wired wrong.

I did a lot of additional reading before I rewired my boat but these should have enough info to explain what you need to do.

https://newboatbuilders.com/pages/electricity13.html

https://www.bristol27.com/projects/b...ounding-system


https://continuouswave.com/forum/viewtopic.php?t=4329


I suspect that’s overkill for the application but again, many ways to do it and very few are correct. If you’re inclined to know the risk and spend a little time reading you can start to see how it should be done. Then if you’re further interested you can read about specifics. Heck, a book can be written on properly crimping connectors and why they’re not soldered. Here’s one example.



https://marinehowto.com/marine-wire-termination/







Elk it’s 2024. We’ve got lithiums now.

But most people here still don't use lithium batteries, because of the cost.

[ghfalls]

100ah life p04 battery on Amazon can be had for $270 and is good for 7000 cycles. At that price, buying lead acid makes no sense any more. In a few years, lead acid batteries will be like incandescent light bulbs.

[Coiloil37]

The inaccuracy is saying an agm will “last the longest and charge the quickest”. Price isn’t relevant but whatever excuse suites the conversation…

Two qualities of lithium, they last longer because they can be discharged deeper and they charge MUCH faster. Maintaining constant voltage to the end helps as well.

[elkhunter11]

Originally Posted by Coiloil37

The inaccuracy is saying an agm will “last the longest and charge the quickest”. Price isn’t relevant but whatever excuse suites the conversation…

Two qualities of lithium, they last longer because they can be discharged deeper and they charge MUCH faster. Maintaining constant voltage to the end helps as well.

There is one more characteristic of lithium batteries, that you failed to mention, concerning marine use, that being that while they are excellent for loads like trolling motors and electronics, they don't like sudden high amperage loads, as in the battery used to start the engine/engines. So while being an excellent choice for deep cycle use, they aren't the best choice for a cranking battery.
As for cost, most people definitely do consider cost to be an important factor when choosing a battery.

[CBintheNorth]

Just run a 12v isolator.
Alternator charging wire to the centre post, one battery on each of the other posts.
Alternator charges both, but each battery can't drain the other.
Starting battery on its own, all electronics on the other.
Downriggers don't draw a lot.