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How to Maintain Deep Cycle Batteries

The Battery Genius knows a thing or two about maintaining your deep cycle batteries.  I’m going to teach you now, but before I do, I want you to realise the importance of doing ALL of these things in order to make your batteries last their longest.  Don’t be that guy in Duluth or Cleveland that does ONE or TWO of these things and then whines because his batteries don’t last. Flooded Deep Cycle Batteries require love.  So I will tell you how to love your batteries well and How to Maintain Your Deep Cycle Batteries.

First, I want all of you to raise your right hand and repeat after me:

“I, (state your name), solemnly swear to trust The Battery Genius do what he says so that my batteries will last a really long time. I will not flake and only do a couple of these things, only to regret it later.”

First things first; New batteries should be given a full charge before use. Yeah, yeah, I know —  your new batteries come from the manufacturer ready to rock-n-roll, but ALWAYS charge your batteries fully before use, please.

New batteries need to be cycled several times (AND NO GREATER THAN 50% Depth of Discharge) before reaching full capacity and hitting their sweet spot — Usually about 20-50 cycles should do it.  Most importantly, be sure to limit how deep you discharge these babies when you first start using them. That’s right.  I said Babies.  Treat them like babies. You have to nurture and work them into the rhythm of how you will use them before you can really start working them.

Batteries should be watered AFTER charging UNLESS plates are exposed before charging.  If exposed, plates should be covered by approximately 1/8″ of water.  Check water level after charging.  The water level should be kept 1/4″ below the bottom of the fill tube in the cell cover.  A Pro-Fill watering system can eliminate the guesswork of proper fill levels and really help with maintaining  your batteries.

Water used to replenish batteries should be distilled or treated to not exceed 200TDS (Total Dissolved Solids…Parts Per Million).  Particular care should be taken to avoid metallic solids like iron.  You’ll hear a lot of old salty battery dudes sitting around your local garage or battery shop sayin’, “If it’s clean enough to drink, you can put it in yer battery.”  Don’t listen to him.  Even if he makes fun of you for driving a mini-van and knowing nothing about batteries, DON’T put tap water or spring water in your battery.  Use distilled water.  You’ll thank me.

Batteries should NEVER be discharged below 80% of capacity (approximately 1.8 volts per cell under normal load;  1.98 volts open circuit; 1.145 specific gravity).  “But, Battery Genius, aren’t Deep Cycle Batteries designed to be discharged and recharged over and over,”  You ask?  Short answer, Yes.  However, anything past 80% DOD is only working them harder than they were designed and you risk speeding up sulfation of the battery plates. Knowing and using the proper battery for the job will help avoid excessive discharge.

Here’s a hint on how to know whether or not you have the right battery bank for the job — If your batteries won’t completely charge in 8 hours, you’re not using enough battery.

In situations where multiple batteries are connected in series, parallel or series/parallel, a replacement battery(s) should be of the same size, age, and usage level as the companion batteries.  DO NOT REPLACE JUST ONE BAD BATTERY!  Never put a new battery in service with a pack which has 50 or more cycles.  Either replace will all new batteries, or use a good used battery(s) with same cycle use.  If you use an older battery with the new, the older battery won’t be able to keep up and will ultimately die or bring the new batteries down to its level, shortening their life.

Please, please, please, test your batteries every now and then (Four times a year).  Periodic battery testing is an important preventative maintenance procedure.  Hydrometer readings of each cell (fully charged) gives an indication of balance and true charge level.  Imbalance could mean that need for equalizing and is often a sign of improper charging or a bad cell.

Voltage checks (open circuit, charged and discharged) can locate a bad or weak battery.  When checking specific gravity, it is possible to convert the reading to what the open circuit voltage should be.  The formulas is to add .84 to the hydrometer reading and multiply by the number of cells.  Thus, a fully charged battery with a reading of 1.265 SpGr will have an open circuit reading of 12.63 volts.

Load testing will pick out a weak or bad cell when other test methods fail.  The point is to look the abnormal.  A weak cell or battery will cause premature failure or erratic function of companion elements such as batteries, navigation systems and other electronics.

DO NOT use a mismatched charging source of any type.  An undersized charger will never get the job done, no matter how long it tries.  An over-sized charger may cause excess gassing and heat that could possibly result in thermal runaway, and explosion! Explosions are bad.

Batteries are like muscles, Inactivity can be harmful to Deep Cycle Batteries.  If they sit for several months, a “boost” charge should be given; more frequently in warm climate (about once a month) than in cold climates (every 2-3 months).

Lastly, just like people, as batteries age their maintenancerequirements change.  Generally, their specific gravity is higher.  Gassing voltage goes up.  This means longer charging times and/or higher finish rates (higher amperage at the end of charge).  Usually, older batteries need to be watered more often or their capacity may decrease.

Hopefully, you’re a little wiser today about your Deep Cycle Batteries than you were before you found The Battery Genius. To BUY Deep Cycle Batteries or any of the maintenance items mentioned here, visit Powerstride Battery for all of your battery and battery related accessories.


  1. Joshua Doty /

    im convinced you know your batteries.actualy my knowledge is growing through trial and error from believing the guy that sounds like he knows.only to find out i was damaging my battery . I have a 12-volt deep cycle marine battery that I use for cleaning pools it Powers my Hammerhead which is a trolling motor with the bag over it pretty much one person told me you was okay to use an automotive starter which prior to charging my battery I read up and found out way off and to have a maintainer. My question is do you charge it on a setting of agm

  2. Joshua /

    Can I pour an electrolyte into my weak deep cycle battery?

  3. My golf cart is always on a trickle charger in garage…..I remove the charger to fill water into batteries….can I then immediately put it back on the trickle charger?

  4. Don Argue /

    RV deep cycle battery constantly needs distilled water. Fill all cells. In 24 hours, water in two cells is down to top of plates or lower. What is wrong.
    Converter sounds like it is constantly running.
    Currently in Banff, Alberta, 600 miles from home in Washington state.
    THANKS for your help!

  5. 2013 Itasca Suncruiser 37F
    Converter never stops running.
    Two (2) RV Deep Cycle batteries (Interstate) are less than 13 months old. Every 24 hours, one Deep Cycle battery has at least 2 or 3 cells that are low on water. So low, I can see the plates.
    What is wrong. Help!

  6. I just bought a trap thrower, they recommend a deep cell 12v battery. I’m a recreational shooter, only a few hundred birds a day when I use it and not every weekend. How should I maintain the battery between uses?

  7. Robert Ellis /

    I have 2 12v deep cycle marine batteries in series for 24v output for a tow cart for a Robinson helicopter. The cart has a built-in charger that I leave on all the time. A pair of batteries lasts only two years. I don’t know it is a float charger or battery maintainer. Should I leave the charger plugged in all the time or is the constant charging killing the batteries? I only run the cart 3 or 4 minutes a month.

  8. This is a very good and necessary idea. thanks

  9. steven spahr /

    I have a 5th wheel trailer that I bought used. It came with a 12V single battery. Want to do some dry camping and are planning to do the following:
    Buy 2- 6v deep cycle golf cart batteries, 100w solar suitcase to charge batteries while dry camping. Here are my questions:
    Do I wire the batteries +to- +to+ and -to-?
    My converter has an option to add a “Charge Wizard” to it, plug and play. Do I need this?
    Is there a special charger I should get to charge the batteries while not in use?
    hould I keep the charger plugged in all the time when not in use?
    Are the battery watering systems worth the money?
    So much to learn. Thanks.

  10. keith hufstetler /

    We have a 24 volt solar system. We have 6 – 8 volt deep cycle batteries. How do I determine what voltage is 80%. 70% or 50% so that my load doesn’t cycle them too deeply.

  11. Robert Pointer /

    I purchased a used bass boat. It has twin deep cycle batteries for the 24v trolling motor. The 24v float charger was used over the winter. When I checked in the spring the batteries were almost empty of fluid. The plates are visable with no fluid around them One puts out 7 volts. Did the float charger boil them dry? It is an expensive charger but now I question the use of float chargers.

  12. shimon russo /

    This is a great site…thanks!
    I am also new to the whole deep cycle battery thing, and here is my question. I have a teardrop trailer with a 100ah flooded type battery. It’s been a week or so just sitting without using anything that is powered by it, and I checked today and it reads 12.1. It was at 12.4 a couple of days ago, and 12.6 a couple of days before that. I guess I’m surprised that it has gone down this way just sitting.
    Should I hook up to my 7 pin connector off my truck and charge it? The sun will be out in a couple of days that will allow me to hook up to my 100w solar. Can I wait or at 12.1 best to charge it sooner with the tow vehicle?
    Thank you very much

  13. jimmy acuna /

    I have 2, 12v batteries for my RV home do i disconnect the batteries when not in use, i use RV 3 times a year.

  14. Robert Ramirez /

    I charged my RV battery’s all three at the same time I got a full reading of 12.73 and 1 days later I got a reading of 12.6 and today I got 12.5 they are not connected to anything showed I be loosing this much V every day.

  15. Dennis /

    I have six 6V batteries, purchased last fall, to run my RV electrical systems when it is not plugged in, or running. I have had it stored for two 1/2 months and apparently left an electric heating unit on. Despite having a solar trickle charger, this drained the batteries to no charge. Are they able to be recharged, or did I just make an expensive mistake?

  16. They call me slick I have three srm 27 interstate battery’s in series which is 36 volts I replaced one of them last year it take longer to charge the new one I had the two older ones checked they checked out fine they both put out 580 amps but I’m not able to fish all day without the the trolling motor going dead the two older battery’s are 6 years old I keep my battery’s charged I’m thanking just because the battery’s tested fine there not able to put out the amperage not voltage all day what do you think

  17. Jim bob shafer /

    I do t see any comments back? What gives?? I do t understand half what you wrote and can barely catch the other half. …. ????

  18. Ken Chadee /

    Thanks for all the info.
    Question: 4 12-volt batteries in a golf cart are used on the golf course 3-4 time per week. I charge them after every use but I leave the charger connected when the cart is not in use. Good or bad?

  19. Peter J. /

    I have a four-year-old deep-cycle battery hooked up to a backup sump pump. It is hooked up to the maintainer supplied by the pump manufacturer. The pump has never been needed, so I assume there has never been any significant net current drain on the battery. I check the electrolyte level and specific gravity annually, and have never seen anything amiss. This year all cells are at 1.270 +/-005. Two of the cells needed a few cc of water to bring the level up to the indicator. How long can I expect this battery to last in its standby role?

    Thanks very much in advance for your informative reply.

  20. Thank you for pointing out that new batteries need to cycle multiples times before they reach full capacity. Getting the best batteries seems like it would be super important. Hopefully, people needing new batteries does some research and finds the best battery for them.

  21. The Battery Genius /

    Hi Ellie, glad to offer helpful info for consumers to get the most out of their battery purchase! Some products simply do better at getting to full capacity quicker and staying there longer. US battery has done a very good job with their batteries out performing the industry in general. Thanks!

  22. The Battery Genius /

    yes, low maintenance batteries need to be properly maintained with distilled water. Maintenance free batteries with calcium in the plates will not require you to add water. These type of batteries are called maintenance free and should be noted as such. With true maintenance free batteries you are not to add water. Powerstide has these convenient commercial grade maintnenance Free and some commercial grade low maintenance options as well!

  23. The Battery Genius /

    Hey Ken, sorry i missed your question before. If you have a smart charger that goes into a float mode then you are good leaving it plugged in. If you are not using a smart charger then you are going to keep an eye on the situation so you don’t over charge and boil up the batteries.

  24. The Battery Genius /

    Hi Jim, missed your comment. Give us a call at – 1-877-576-9379. We will try to answer any questions you might have. thanks!

  25. The Battery Genius /

    Those batteries can in theory just keep going. If they are not getting discharged much at all and you have a maintianer on them then you will get long life from them. I assume it is a deep cycle battery you have there and can be supplied water when and if needed. I don’t know if i could predict the number of years in total, but i don’t see those batteries going bad for a long time since they are not really getting discharged other than natural 3% per month which is being restored by your maintainer. Let me know when they die out finally. Thanks!

  26. The Battery Genius /

    Yes, golf cart batteries are deep cycle and do a number of cycles to reach up to their full capacity.


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