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Author Topic:   Replace 1 out of 2 Optima Batteries?
andygere posted 08-26-2013 08:22 PM ET (US)   Profile for andygere   Send Email to andygere  
I have a pair of Optima Blue Top 34M batteries that have been in service since I bought them at Costco in 2006. Recently, the house battery is showing signs of wearing out. I am beginning to get low voltage alarms on my chart plotter, indicating that the house battery is dipping below 12 volts with light accessory loads when fishing. Earlier in the season, I charged it with a 10 amp battery charger, and it seemed to hold the charge, however that appears not to be the case anymore. The dedicated starting battery continues to hold charge, and showed 12.4 volts after over a month of inactivity. Note that at the start of the season, I checked and cleaned all terminal connections and inspected the wiring, all of which is in good condition.

I'm considering moving the start battery over to the house circuit, and purchasing an identical (or the current available equivalent Optima) since the start battery seems to still have life to it. Is there any fatal flaw to this strategy? The batteries are charged via a voltage sensing relay circuit, and the starting battery is isolated completely from the house loads. My thinking is that if the original starting (now house) battery shows weak performance, I can always purchase a second new battery. At over $200 per battery, I'm not anxious to retire the one that seems to be still performing well.

Eagleman posted 08-27-2013 08:40 AM ET (US)     Profile for Eagleman  Send Email to Eagleman     
Your exchange of batteries sounds valid however with approximately 7 years of service on the batteries you're up against the normal life of even the best batteries on the market. I went through the same battery switching around recently I got anther year out of one but that one failed after anther year of service. 8 years of service is most I've ever gotten out of any quality battery.
tmann45 posted 08-27-2013 10:31 AM ET (US)     Profile for tmann45  Send Email to tmann45     
If you don't have any mission critical loads on the house battery, definitely make the swap buy only one new battery.

Do you keep your batteries topped off with a charger? If not, I suspect that your house battery might not be getting a full charge thru the battery combiner when just charging with engine running due to you saying it held a charge after putting it on a charger.

andygere posted 08-27-2013 11:38 AM ET (US)     Profile for andygere  Send Email to andygere     
Eagleman, I suspect I may wind up there, perhaps getting just another year out of the start battery. These Optimas are combined start/deep cycle batteries, and since the E-TEC starts to quickly and easily, I think the start battery has gone through fewer and much shallower discharge/charge cycled. The largest house battery loads are the downriggers, but when I'm trolling on the kicker, they will certainly draw more power than the tiny alternator on the kicker can replenish. We typically check the trolling gear for weed and jellyfish every 15-20 minutes, so that's 3-4 up and down cycles per hour for each downrigger. If it's foggy and the radar is on, the load is even heavier. Radio, lights and other electronics are the remaining loads.

tmann45, When the main engine is running, I see over 14 volts on the house circuit, so I'm certain that the charging system is working correctly. The battery switch cluster has an LED light that indicates when the VSR is engaged, allowing current to pass to the house battery. This lights up a few seconds after the engine starts every time. One of the really nice things about the Optima AGM batteries is that I have found they do not need to be topped off with a trickle charger. They hold charge even after longer periods of non-use, which is one of the reasons I'm willing to pay more for them than wet cell batteries.

Checking the Optima web site, I see that they now offer a blue top Starting specific marine battery. It is less expensive than the dual purpose batteries, and has a slightly higher CCA rating. I may replace the old starting battery with one of these, and move it over to the house side and see what happens. Is anybody using an Optima 34 M Starting battery?

OptimaJim posted 08-27-2013 02:49 PM ET (US)     Profile for OptimaJim  Send Email to OptimaJim     
Andy, just so I'm understanding what you've posted, the BlueTops you currently own are both D34M models, as noted by their light gray case? The 34M BlueTop is a starting-only battery and is identified by a dark gray case.

I would suggest fully-charging your D34M batteries to about 13.0-13.2 volts and have them load-tested. That would give you more of a picture of battery health. As long as the two batteries are properly-isolated from each other, you can run dissimilar batteries. If they are not isolated, they need to be identical in age, size and type.

The 34M will offer more cranking amps at the expense of some reserve capacity and the ability to be deep-cycled. Fully-charged, those batteries will measure about 12.6-12.8 volts. If you have any other questions about our products, I'll do my best to answer them.

Jim McIlvaine
eCare Manager, OPTIMA Batteries, Inc.

andygere posted 08-27-2013 06:36 PM ET (US)     Profile for andygere  Send Email to andygere     
Jim, thanks for that information. You are correct, the pair that I currently own are the light gray case dual purpose start/deep cycle models.

They are isolated with a BEP Marine VSR switch cluster 716-sq-140a-dvsr-single-engine-two-battery-banks and wired so that the only load on the start battery is the main outboard motor, with all house loads and the starter and charger from the kicker motor on the house battery. The only time they would not be isolated is in the instance that the house battery was used to "jump start" the starting battery by activating the emergency parallel switch. Here's a link to a diagram showing how they are rigged. BEPwiring.jpg

Is this isolation sufficient to operate the two different battery types?

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