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Put a CHARGE into your Summer!

Put a CHARGE into your Summer!

Apr 18, 2012

Hey, before you read this post, do me a favor go get two glasses of water and an eye-dropper before reading on about Marine Battery charging.

No, no. That’s okay. I’ll wait. Seriously…


First, choose one of your glasses and name it “My Marine Battery.”
Now, drink half of the water out of that glass called your “Battery”.

The remaining water in your glass is just like the remaining capacity in your battery every time you get back from Lake Nocareintheworld and your Flooded Marine Deep Cycle Battery is now at 50% Depth of Discharge. Well, your flooded battery will lose a half to 1% of its remaining charge per day just sitting there until you put it on a charger before your next run back to the Lake.

“That’s okay,” you’ll say. “I’ll just hook it up to this handy Trickle Charger I bought at the discount store for $39.99.”

That’s what your eye dropper is for.

Using your eye-dropper, begin filling “Your Battery” with the other glass of water…I’ll wait.

How long do you think that will that take?

More importantly, how likely do you think it is that you’ll ever fill that “Battery” back up before you get thirsty and start drinking it? Want me to continue..? Oh, alright.

You see, The Battery Genius knows a thing or two about maintaining Marine Batteries and I’m here to say, unless you’re pumping at least 14.4 Volts into your Marine Battery – IT IS NEVER GOING BE FULLY CHARGED EVER AGAIN. 


Never never ever.

Battery manufacturers’ specifications say that a standard 12 Volt Battery needs to be charged anywhere from 14.4 to 14.8 volts (14.7 specifically for some AGMs like Lifeline) and then maintained at that level for AT LEAST an hour, before it will be at 100% capacity again. What’s 100% capacity, you ask? 14.4 Volts. Heck, if you’re not hitting at LEAST 14 Volts, you should go to Vegas. It’s more fun gambling when you might win something.

Dead Battery + Dead in the water = NO FUN. I oughta know.

The MOST and I mean MOST you’ll get out of your INITIAL bulk charge from your $40 trickle charger is 13.6 Volts. What are you gonna do with 13.6 Volts? I’ll tell you – Your going to be repeatedly heading out onto the lake with a diminishing battery that will never last through the summer. Because next time you’ll go at 90%… drain it. Charge it 85%… drain it. Charge it 70%. You see where this is going? Your Trickle Charger doesn’t initiate at a high enough VOLTAGE to bring your battery back. What’s worse – It’ll just switch off when it gets itself reading “full” and never tell you HOW full your battery is. Or isn’t as this case would be.

The BEST way to charge your marine battery is to use an On Board Charger. This is a permanently installed charger that you plug into shore power whenever you aren’t using your boat to maintain your batteries. Unless you are on the water ALL THE time, it may be a little out of your price range.

Associated Equipment makes a terrific bench-top charger  – The Intellimatic – great for Lead Acid Batteries of all kinds (deep Cycle or Starting).  They are available in three different models (Flooded Batteries, AGM & GEL) and all are made in the USA by Associated Equipment.

To get the very best advice on charging, maintaining, or buying Marine Batteries, call the folks at Powerstride Battery. They love talking about this stuff. Plus – its FREE for you: Toll Free (877)576-9379.


Most “smart chargers” are extremely stupid when it comes to determining what “Fully Charged” is and shut off at 13.4 Volts.
Fully charged is 14.4. Period.
Got it?

Now go get some sun. You look horribly pale.


  1. Laura /

    Thanks for educating me and making me laugh at the same time! Now I need to go see if this charger we bought is up to the task.

  2. admin /

    NOCO Genius Chargers are great! I forgot to mention that!

  3. paul schultz /

    I have a marine deep cycle. It was mysteriously tipped over….and lost some acid. How should I refill it? Do I need to get acid or distilled water?

  4. One should always – (almost) ALWAYS – use distilled water when replenishing the electrolyte in your battery.
    Especially when that losst electrolyte is from gassing.
    HOWEVER, if it were tipped and spilled, adding electrolyte is in order for an older battery (a year or more). BUT it must be 36% Sulfuric Acid (SO4) and 64% Distilled Water (H2O) AND Maintain Specific Gravity of NO MORE of 1.270 when fully charged… NOW – MOST new-ish batteries won’t be affected by just adding distilled water to make up the balance. Just top it to a quarter of an inch above the plates and give’er a full charge and see what it reads. TBG thinks you’ll be fine with the H2O without having to add electrolyte.

  5. Robert /

    I have a 95 RV that is only used in the summer. I usually take the 2 deep cycle batteries to get professonly charged at the beginning of summer. I just pulled them out and both are bone dry of water. I filled with distilled water and hooked up a 25 amp charger and within 15 minutes the charger went blank, like no electric. I check and the outlet had 110 volts. Did the Batteries cause the charger die?

  6. The Battery Genius /

    @Robert – the charger probably didn’t “die” but it does probably need to detect a nominal voltage to work. Or it may be programmed to shut itself off to protect itself from shorting out if voltage isn’t detected.

  7. Robert Johnson /

    Hello Battery Genius. I have a BatteryMinder Model 2012 which is a 12 Volt maintenance charger with full time desulfation hooked to my Interstate Marine/RV HD 24 DP battery when not not being used in my pop up camper. I have read some of your comments that you do not recommend leaving the battery hooked up these devices for extended periods of time. Are you familiar with this device and if so would you still not recommend extensive charging as this device recommends? If you do, how would you recommend I use the BatteryMinder to adequately keep my batter charged?

  8. Mike Dejno /

    One of out maintenance tech’s decided he would get more life out from our fork lift if he installed a deep cycle battery, He did this about a month ago. By the way this is a propane lift not electric except to start. I was doing a compression test on the 4 cylinder Toyota lift, while cranking the motor over (coil wire off) the battery exploded not good. was this a mismatch charging problem ? in 30 years I have never heard of this happening.


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