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Author Topic:   Battery charging protocol
Frank O posted 08-26-2006 10:27 AM ET (US)   Profile for Frank O   Send Email to Frank O  
I was just reading the thread on carrying a jumpstarter backup device, and can see that though a unit like that might be occasionally handy, the first priority would be to make sure the boat's installed batteries are in optimal shape. But this then led to a question I've been wondering about regarding battery charging strategy.

My 1995 21' Outrage has two batteries with the usual 1-ALL-2-OFF switch. I understand that it's a bad idea to run with the switch set to ALL, as it's not desirable to charge two batteries connected in parallel from the same source (the alternator in this case, though this would also apply to a charger). Logistically it'd be tough for me to leave the batteries on trickle chargers at the dock, or top up with an external charger before we run.

Most of my boating involves running for 20 to 45 minutes to a dive site, sitting there for a couple of hours with radio etc on, and then running back. Boat outings might be once a week, or 2-3 weeks apart.

So I'm trying to think through an approach that will keep both batteries in good shape. If I run with the switch set to charge one on the way out, and the other on the way back in, would that do it? Or do I need to rethink putting trickle chargers on them at the dock?

DANO posted 08-26-2006 10:58 AM ET (US)     Profile for DANO  Send Email to DANO     
have you thought about using a deep cell for your time at the dive sites? plenty of reserve to power the radio.... and when you want to leave, turn the switch to your starting batt. and then to "both" after you are running to charge.
Frank O posted 08-26-2006 11:28 AM ET (US)     Profile for Frank O  Send Email to Frank O     
Thanks for the reply, Dano. I believe both the batteries on the boat would qualify as deep cells.

But your comment about setting the switch to "both" while running is exactly what I was getting at. Although this seemed like a good idea initially, I understand it's not a good idea to run with the switch set to "both."

DANO posted 08-26-2006 02:13 PM ET (US)     Profile for DANO  Send Email to DANO     
Frank, I'm not sure why you can't charge both batteries at the same time off the same charging circuit. If the charging system is capable of at least the amperage rating that the batteries need to charge, I don't see why this is not possible. If you discharge the batteries to a lower than normal level, then start your engine (provided there is enough reserve to do that) and run a multitude of electrical items, if the charging system is not capable of providing the necessary amount of amps to 1. run the electrical items, and 2. charge the batteries, then I can see a problem. Obviously a slow and certain death for your battery, due to the lack of recharge. I can't think of anyone that I know that does'nt run their battery switch in "both" position when underway. At anchor, overnight, with a radar and watch circle running, an anchor light, and perhaps a radio, different story. but I hope someone else out there chimes in and sets me straight if I am wrong...
Bulldog posted 08-26-2006 04:26 PM ET (US)     Profile for Bulldog  Send Email to Bulldog     
Frank , you should be fine running with the switch on both on the way in and out, although you might want to switch to just one while out there. I have twin engines, with sepearte systems, in that case it is a no -no to run the switch in the both postion. Former owner of my boat learned this, tieing two charging systems together with motors that can run at different RPM is not good!....Jack
Frank O posted 08-26-2006 04:49 PM ET (US)     Profile for Frank O  Send Email to Frank O     
I'm not the expert on it, but my understanding is that if you take two batteries that differ in age or performance and charge them in parallel from the same source, there are potential problems -- charging can cut off before the newer one is fully charged, or the older one can end up getting overcharged (meaning getting really hot, safety problems, etc.).

But I imagine a lot of people get away with charging in parallel, particularly if the batteries are close in age and performance.

I can't say I have real-world experience on this with boat batteries, though I've run into issues with battery packs for high-intensity dive lights. These battery packs are typically made up of parallel strings of cells, and when some of them start getting old and don't perform as well, the battery pack ends up unbalanced and problems ensue. I've found this can lead to incomplete charging, or at worst batteries that get really hot. Although most divers just charge the cells in parallel, my purist friends who work in electronics tend to rewire the battery packs so that they can charge each string of cells separately.

cwolf posted 08-31-2006 02:37 PM ET (US)     Profile for cwolf  Send Email to cwolf     
One option you may consider is the new Blue Sea Dual Circuit Plus switch and a Blue Sea ACR. I recently changed my battery setup to this system and it really works great. I have two batteries, one for starting and the other for electronics/lights etc. The Dual Circuit switch is a off/on/combine switch where I had the standard 4 position before. Batteries are now on their own dedicated circuits with this switch and can be combined in an emergency. For charging the ACR first charges the starting battery until proper voltage level is reached and then switches to the electronics battery. I used to always forget what switch I was on or what battery needed to be charged with old setup. This system makes it a no brainier. Just turn switch to On and go.

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