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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. The Battery Genius /

    I never – NEVER – no matter how “automatic” it is, leave a battery hooked up to a float charger. I just don’t. NO good reason, except there’s just no reason to do it and I’ve never had an issue with batteries going dead.

    Fully charged off the charger should be anything above 13.5 13.8 for newer batteries – that stabilizes to 13.2+ over night.

    Can’t hurt to invest in a new battery… Just don’t know that an old(er) battery is a reason to get a new one, unless you always want your batteries to perfom like new.

    A trickle charger/maintainer keeps a Fully Charged Battery charged… The problem is that a lot of Low Maintenance Batteries dry out after 25 days and continue to gas at higher rates as they dry out which also helps to speed the diminishing voltage. Best bets, Charge your battery fully. Store in a dry place and check it every month. Give it a boost charge. Check Water. Repeat.
    Or, buy AGM… they have a considerably longer shelf life in fully charged condition with minimal self-discharge.

  2. The Battery Genius /

    @Dave – another couple of years… maybe 4.

  3. The Battery Genius /

    @Christine — the solar panels you wnat are so discrete on top of the camper, one would never know they’re installed.
    The only caveat is the wire leading to the batteries.

    You are absosmurfly correct. Fully charge your batteries. Then, connect them to the solar charger.

  4. Thanks very much, I appreciate you making this post available, the
    rest of the site is also done well. Have a nice day. Cheers!

  5. If I connect a harbor freight float charger to a solar panel then connect those clip from the float charge to the rv battery. Why does my float charger drain the battery?

  6. The Battery Genius /

    @ Mr. Lee – I dunno.
    Why would a person need a Float Charger AND a Solar Panel connected to a battery?
    My first guess is it could be that you’re not “draining” the battery as much as you are overcharging it.
    The main argument against continuous float charging is that the battery will: a) be undercharged, or b) be overcharged, and / or c) be permanently damaged as a result of a) or b).
    I wouldn’t trust a $10 Harbor Freight Float Charger to do anything Automatically except be a paperweight.

  7. Kevin Reardon /

    I have a cabin which I have two deep cycle batteries for lights,phone ect ect ect,my question is since we DO NOT use the cabin during the winter months,the batteries are connected to solar panel with charge controllers, keeping them connected during these winter months,would they stay warm instead of disconnecting them and lugging them home after every season,the cabin is insulated and temps drop down around 20 degrees inside the cabin

  8. The Battery Genius /

    @Kevin – Sorry. You gotta lug em out and keep them warm and maintained.

  9. David Heller /

    I am installing 20 L16′s, 5 strings of 4 in a 24 volt system. How do I go about fully charging them before charging them with my solar panels? Or can they be fully charged by the solar array?

  10. allen /

    I just bought a deep cycle battery (alphaline xv31) with the purpose of discharging it pretty low. I assumed discharging till there was 20% charge left would be ok for those batteries but as I read this page I learned that they will get damaged doing that. The battery will be used for powering phones or small speakers in the woods or having a party at the beach and plugging it to a receiver (using a pure sine wave inverter). How bad will the battery be damaged as I calculated to go as low as 20% charge left. And what better solution is there for portable energy without the use of sun or a generator? Thanks in advance

  11. Lynne in Florida /

    The batteries on my 24v wheelchair system were replaced with new two months ago. I normally re-charge them when the meter on the controller reads yellow under heavy load (going uphill, for example), but green otherwise. Yesterday I, out of dire necessity, was forced to run the batteries waaaay down, showing red under heavy load, and yellow otherwise. I had an interval of about two hours when I could use the charger, which was operating normally, then had to use the chair again, though only for a short distance, but again resulting in showing red under heavy load.

    Normally the charger lights a red led to indicate ‘power on’, and a second diode to indicate ‘charging’ (yellow), and ‘charge complete’ (green).

    Now the charger, when fully connected, shows only the red ‘power’ light, but will not activate the second diode, the fan does not come on, and the controller meter does not peg out as it normally does when charging. (I don’t normally re-charge with the key on, but will flip the key to read that meter occasionally.)

    Do you think my problem lies in the charger or the batteries, and what can I do about it?

    Thanks for your help.

  12. Thank you for posting this information. Can I charge my batteries with a portable charger WHILE the inverter and controller are still connected to the batteries? I occasionally need to supplement my solar panel charging with a regular charger due to weather, camping in woods or just plain using too many amps. I have two 100 amp batteries connected in parallel. I would like to bulk charge at 15 amps until 90% charged, then let the panels do the rest. Thank You

  13. The Battery Genius /

    Absolutely… as long as the total voltage does not exceed manufacturer recommended charge voltage!

  14. The Battery Genius /

    Most “automatic” chargers must detect a nominal voltage of “X” number of volts to turn on… If your batteries were discharged too low, your automatic charger won’t turn on to charge them! Take them OUT of your chair and put them on a bulk charger.

  15. The Battery Genius /

    How bad it may be damaged depends on the battery, construction, temperature… a lot of things. What better solution…? Use a bigger battery.

  16. The Battery Genius /

    They should be FULLY charged new coming to you.
    Get a series charger or string charger and give em a boost before installing.
    NORMALLY< most solar systems have an equalize setting… Use this when first hooking them up and you’ll be good to go.

  17. Mike of Florida /

    I have installed a new 36 volt array of 6 v batteries in my old ez-go golf cart. I made sure to thoroughly clean each battery cable connection and replaced two of the damage cables. I checked and brought the distilled water to servicable level in each cell. PROBLEM: when I connected my charger to the cart it would not kick in the charging process. I’ve heard before and read in your website that if the voltage is to low for te charger to detect it will not start.
    I’ve also heard that you can “jump start” the array via a separate charging source sufficient for the regular charger to work. I’m assuming that if I use my other car battery charger with a 6v option switch and charge vs start switch placing the positive on one end of the array and negative on the other end, that it will give me the boost charge to get my cart charger to work.
    Am I right? If not please advise on next avenue of solution. Mike

  18. sarah /

    I have a small cabin powered by a generator powered battery bank of 8 deep cycle batteries. I will not be using the cabin in the winter. How do I winterize the batteries?

  19. The Battery Genius /

    @ Sarah -
    Make sure they are fully charged.
    Disconnect them – typically just the negative cable to the main supply works, but TBG recommends disconnecting each battery completely.
    Insulate them – below, above and around with battery blankets or other insulated material and keep them above 45 degrees
    If possible, top charge every 30 days.

    Happy Winter!

  20. The Battery Genius /

    You are right… charge away!

  21. I’m getting ready to shut down my battery bank for 3-4 months. I have 48 2 v batteries . What would be the best way to keep the batteries safe ?

  22. The Battery Genius /

    Not ideal, but:
    Fully charge them. Disconnect them. And keep them dry and in a temperature controlled environment.

  23. Good article! Evereone should follow these steps to maintain a deep cycle battery. Definitely going to recommend it to others.

  24. vicperuzzi /

    I have 8 deep cycle batteries. im replacing all of them.1 should I charge all of the new ones after I install them or charge them separtly? once they are installed can I constantly connect it to a 110 v source when not in use? please advise.

  25. I bought a new John Deere electric gator 9/13. The first two times charging I would get 3.3 hours run time before needing a new charge. But after running batteries so low that I needed a tow back to recharge. I now only get 1.1 hours of power before I need to recharge.this is a 48volt system and when charged its 48+ volts. But lose power too quickly. Should I replace batteries??

  26. I just purchased 2 new batteries for my boat. (10-12-13) . Do they have to be trickled charged over the winter. Until I put them back in mid April?

  27. The Battery Genius /


  28. The Battery Genius /

    Check your charger and the charge rate… If they’re new, the batteries prolly aren’t the issue.

  29. The Battery Genius /

    @vicperuzzi – New batteries should always be given a full charge before use. Your second question depends on the charger… is an automatic charger? constant voltage? Variable? Check your owner’s manual or consult your local mechanic.

  30. I’ve just got back from my boat which is overwintering.
    Someone had disconnected my battery charger which has resulted in the battery (deep cycle) fully discharging (showing about 7 volts).
    I’ve reconnected the charger supply (3 stage charger) but I’m concerned that the battery might be ruined.
    Any advice?

  31. The Battery Genius /

    Dave, you’ll have to connect a battery in parallel to fool your charger into bulk charging.
    disconnect the Second battery and do a deep recover at 15.5 Volts for 6 hours. That might bring it up.
    Doesn’t look good, though. The patient is critical. :(

  32. Cody B /

    If Power Inverters have an automatic shut off at 10.5 volts, why does it take so long to turn off – if you were to wait till 10.5 on your deep cycle batteries you pretty much toasted them. Why don’t they shut off at 12.1 which is 50% of the discharge so people won’t undercharge their batteries. Can I adjust my power inverter to disconnect at 12.1? I have a Whistler Pro 1200 power inverter and pretty happy with it.

  33. I have a PJ dump trailer with an electric over hydraulic dump system. Battery in trailer is dcm battery and is connected to a wire from the truck battery via trailer plug. This all worked fine for a year or so, then a short in the wiring drained the trailer batter completely dead. I charged the battery with a 10 amp charger over night abd it dumped three or four times and was by then, too low to dump again. I have re-charged this battery several times, with the same 10 amp charger, and even though it is a 45 minute drive to the landfill, after three trips the battery needs charging. What is wrong here? Why is this battery draining so fast> I even went back to the automotive store and replaced the original battery, then in about 4 months, I replaced it again, but still, nothing makes a difference. The battery is still low after three dumps, despite the time it remains connected to the truck. It never affects the batteries in the truck, just the battery in the trailer. What do you think is going wrong?

  34. The Battery Genius /

    The battery should be connected directly to the alternator. If it isn’t, it may not be getting charged properly.

  35. The Battery Genius /

    @CodyB – Dunno. That sounds like a question for the inverter folks…

  36. Hi,
    Based on your write-up…… please what is the remedy for a new deep cycle battery that has been used deeply before the first charge?

  37. Sounds like a great product!

  38. Ben /

    On delivery of 36 Beneteau. 3 year old start battery was toasted when we started in the Caribbean, but worked. Now in New England waters it won’t start the diesel…we are guessing due to temp drop. I changed the cables over to the 100Ah house bank. Engine started once. Next time, house bank could not supply enough energy to start. Solar panel charges house bank. HB is flooded, 6 cell, 12 v. Question is, how much damage can we do to the house bank by trying to start diesel? I do realize the hb is painfully undersized.

  39. Richard /

    I just bought my first travel trailer. Like an uninformed dummy, I ran my single group 31 battery to dead, twice. First question, is it ruined? Second question, if I have to replace it, can I go with an 8D size to double the amphour or do I have to stick with the same size? (I’m not sure that I have the room for dual 31′s.) Thanks!

  40. daryk /

    Is it bad to top off voltage. I have a brand new maintenance free battery that I troll with. Want to dish in the morning and my voltage is at 11. The only thing is my trolling motor is my only motor, so I don’t want to get stranded on the lake

  41. The Battery Genius /

    Never bad to top charge! Your Deep Cycle batteries should be charged after each use!

  42. The Battery Genius /

    Probably not “ruined” but anything past 80% DOD repeatedly is not good for batteries.
    If you have room, you can use whatever you want. Just make sure your charger has enough juice to replenish an 8D in a timely manner!
    (unlike my reply to your comment… sorry!)

  43. The Battery Genius /

    Not much damage at all! One or two starts won’t hurt you… Just don’t make it a habit!

  44. The Battery Genius /

    Equalize the battery using the factory recommended Equalization charge profile.

  45. donald /

    I have a kinetic 1800 (car audio) battery I load tested it an dropped to 4.9 is it junk junk or would I be able to put it on a slow charge for a day a n be bk .

  46. The Battery Genius /

    Sorry… 4.9 is toast. Have that battery recycled somewhere locally and find yourself another good deal on an AGM Battery here:

  47. Mark /

    I have two car batteries and the cells are completely dry. If I refill them with distilled water and charge them will they be okay? Thanks

  48. The Battery Genius /

    Probably not. It’s worth a shot, but you’re prolly going to have to buy some batteries :/

  49. Mark /

    I use the batteries for my camper but what do you recommend, should I ditch the batteries and buy new or try to save them?


  1. NOTHING Should get Between you and your weekend! | The Battery Genius - [...] March, I told you how to maintain your deep cycle batteries.  (If you didn’t read this post, please bookmark …

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