Rotating the tires....er, ah, batteries?

[rpmerrill]

It's been wicked nasty hot here this summer and we were out of town in search of cooler weather for a couple weeks this month. While traveling, thoughts go through my head, day and night. I've never been an idle time guy. In the "boat" category, I began to generate questions about my batteries.

I have 4 AGM batteries on my R-27. Previous owner installed them before he sold it to me, so they are relatively new. One battery each for engine and thruster. Two batteries for the house.
I hear that boat batteries get pretty tough duty and don't last all that long, however. I know that some batteries are good at big amperage draws and some are good at deep cycles. Not sure what AGM's are best at... I read it once, I think. I've also read that you should replace the batteries as a set.

Anyway, looking at the duty cycles, I'd say that engine and thruster are subjected to big amp loads. Thrusters may be worse? Dunno. House batteries are subjected to deep cycles. Am I correct on that ?

If so, I'm wondering if it makes sense to rotate the batteries to prolong their life (as a group).
Am I the first one to ask this question? Is it totally a crazy idea? Would it work?
Cool weather is coming soon and I'll stop asking these questions, at least for a couple months.
Let the discussion begin.

 

[Cutwater28GG]

not sure I would want to mix up different aged /abused batteries in the same house bank. I treat the house batteries as one unit. otherwise the stronger battery will push power to the weaker. moving the single engine and thruster battery would be less of an issue. but then I'n not really sure its all worth it.

 

[NorthernFocus]

As said, bad idea for batteries in a parallel bank. OK for single batteries but probably no benefit and/or not a good idea either depending on how they've been used.

 

[knotflying]

I wouldn't rotate them. However, your point about the thruster battery is something I have always thought about. It gets a large short burst of use, similar to starting an engine. Why wouldn't one use a marine engine start battery rather than a deep cycle? On the other hand, I have joined my thruster battery to the house bank with a switch in between so I can still isolate the thruster from house. I usually just keep them joined and have never really had an issue. As a matter of fact, I find the thrusters run much better having the house connected. I have had this configuration for 5 years and no issues.

 

[rpmerrill]

By joining them, the primary point being more amp-hours available to the house? Or better current rush to the thrusters?

Either way, sounds like a interesting twist.
Gotta think about that one for a bit.

Only downside might be low (or no) emergency juice available to start the engine with the parallel switch.
I'm not sure how big a deal this might be. I've only used my parallel switch once and that was on first start after a winter storage and that was only a precaution that I thought was a good idea at the time.

I like your idea more and more.
Thanks

 

[BB marine]

I use a similar method of Mikes battery arrangement . House and thruster parallel through my inverter battery switch. We do not have a generator so all 120V is provided through the 2000 Watt inverter. When cruising I have the battery switch on both giving 300 ah when demands are required and the engine alternator is maintaining the batteries. This gives a little extra boost to the thruster when needed and also to the inverter and other house requirements. When at anchor I have inverter switched to house batteries switch is turned to 2 position. If my voltage drops to low from house and inverter usage I still have a fully charged thruster battery that I can parallel to the circuit. I also can use it for an emergency start for main engine battery by switching to both and using crossover switch.

.

 

[Osprey]

It is pretty hard to reach a consensus with respect to the best battery type and configuration. In my R27 (factory build in late 2011), the factory installed 4 AGM batteries in the standard battery configuration: 1 thruster/windlass, 1 starter and 2 house. I changed the configuration by paralleling the thruster/windlass battery with the house pair. For thruster operation, always with the engine running, I have the 150A alternator along with 3 batteries to provide the required current. For multi-days at anchor I have 3 house batteries to meet the extended demand without excessive discharge of the house set. I might add that my tug has a factory installed 135 watt solar panel and last winter I added a 200 watt panel. With the original panel the house set was good for up to 3 days at anchor. Now with the added 200 watts, the panels provide all of the daily power requirements. For sunny days, that is. For "dark" days I sometimes run a 2000 watt Honda generator on the swim grid. About a 1 hour run feeding the AC into a 20A and a 30A battery charger, yielding about an initial 50A total battery charge current. I also use the generator for the occasional requirement of 120V AC to run appliances such the microwave or the wife's hair drier.
I am now well into the 2018 boating season still using the original AGM set. I have never discharged the house set, of 3, below 50% depth of discharge . As an estimate I would say that the house set have, so far, gone through about 500 charge/discharge cycles. As a starting backup I have on board a "NOCO Genius GB70" lithium ion jump start battery pack. This booster can produce a peak current of 2000A at 12V. Never had to use it on my tug but I have used it to help others.