Batteries just not holding a charge

Does this always mean you need to replace the batteries?
The system is 4.5 years old. We lose power everynight if we don't charge with generator before bed.
Any advice would be great.


  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Batteries just not holding a charge

    Did the system ever work properly? (i.e. handle loads from charge to charge).
    Have you added any additional loads?
    What type/size (Amp hour) batteries and how many?
    How big an array have you got for charging?

    Some batteries will be dead at 5 years no matter how well you look after them, others will last several times that long if well maintained. Any battery habitually under or over charged or drained beyond its maximum depth of discharge will have a shorten life.
  • System2
    System2 Posts: 6,290 admin
    Re: Batteries just not holding a charge

    Yes it did work great when it was first put in. In the last year it just isn't working as well. We had someone look at it last summer and he said 3 of the batteries were bad so we replaced them and it still didn't work right.
    We have 16 batteries and 16 panels.
  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    Re: Batteries just not holding a charge
    We have 16 batteries and 16 panels.
    That is a lot of batteries and it is not often good to mix old and new batteries together. I would suspect that you have still more batteries going bad and they will pull the new ones down to their level. You might consider larger and fewer batteries for your system. This gives you fewer connections to go bad and fewer cells to maintain. What voltage is your battery bank and how large are the batteries.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Batteries just not holding a charge

    To give you a more complete answer, we'd need to know the type of battery: Flooded Lead Acid. AGM, Gel - are they true deep cycle or a "Marine/RV" or automotive (not recommended) or what? And how many Amp/hrs capacity, Voltages, et cetera. Also the specs on the rest of the system (panel Wattage, system Voltage, charge parameters).

    But in general, you should replace a battery bank as a whole. Replacing just three probably won't be much help because the others are old and close to failure and will draw the new ones down.

    It is more important at this point to get the technical details together and try to determine why the batteries failed at 5 years.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Batteries just not holding a charge

    More detail please!

    My intuition is (no offense intended) is that you might not know enough about how and why your system works to get maximum performance out of it. I would suggest that you start here:

    I think you have to get a good understanding how your system works, how much power you can realistically expect to get out of it on an average day/week etc.

    Depending on battery design, 5 years might be a reasonable life span, or it my well be that you have killed them way to prematurely. By reading the links above, it will give you a good idea of what you might reasonably expect.

    Also, please read the links to understand the efficacy of adding new batteries into old strings. Not generally a good idea, but may in some circumstances be acceptable.

    Good luck, please provide some more info, and welcome to the site,


    PS 16 panels/16 batteries doesn't mean much. Panel capacity/ battery AH capacity expected loads etc are a much more important detail than just the number of batteries/panels.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    Re: Batteries just not holding a charge

    Typically, 4-8 years for an average Golf Cart deep cycle battery bank is probably about right. Other (more expensive) batteries may last 10-15-20+ years if well taken care of.

    A couple of good Battery FAQ's:

    NAWS (our host's) Battery FAQ

    For the most part, people cause early death to their battery banks through:
    • under charging/deficit charging--basically, just not recharging the battery bank fully--but instead running it under 75% state of charge for long periods of time (sulfate begins to harden below ~75% SOC--do not spend more than a few hours/1 day below to minimize--weeks-months below 75% SOC will kill the bank).
    • overcharging--excessive equalization (charging above >~14.5 volts (for flooded cell, bit lower for AGM/Sealed which should never be "equalized". Flooded cell batteries tend to corrode the positive plates (may see positive posts rising, top/sides of batteries expanding).
    • Improper filling--letting electrolyte fall below the top of plates and/or filling with "dirty" water instead of distilled or filtered rain water.
    From this thread:

    I like Dave Sparks' post:
    I learned this strategy from Dave Surrette (Rolls) in the late 70's. Pretty much the bible on how I design my systems for off-grid.

    Assume that the system will never reach more than a 90% state of charge.
    Try not to go below 50% SOC, ever! Complete absorption over 90% of the year

    Use the energy stored from 70% to 90% SOC for your daily cycles.
    Save the energy from 50% SOC to 70% SOC for aging to get long battery life.

    I know Surettes has changed their recommendations over the years but I also know they are in the business of selling batteries! If you do the above you will get 10 to 15 years on their batteries with decent maintenance.

    The OP is making it complicated by mixing battery types and not really stating a lot of information that would allow decent specific advice.

    Oh yea, I am really happy that Surrette and Trojan are making L16's with 1000 AH capacities @20HR. Been bugging them for many moons to do batteries less than 125LB's!

    And, my two cents... If your batteries are using a bit of distilled water per month--you are probably OK. If you are using none, or a lot per month--then you are probably under or over charging.

    Add the Trojan recommendations here:

    From Trojan's battery manual (PDF):
    Equalizing (flooded/wet batteries ONLY) 3.4.2.

    Equalizing is an overcharge performed on flooded/wet batteries after they have been fully charged. Trojan recommends equalizing only when batteries have low specific gravity, below 1.250 or wide ranging specific gravity, 0.030, after fully charging a battery. Gel or AGM batteries should never be equalized.
    • Confirm that the batteries are flooded/wet
    • Check electrolyte level to make sure plates are covered with water before charging
    • Check that all vent caps are secured properly on the battery before charging
    • Set charger to equalizing mode
    • The batteries will gas (bubble) during the equalization process
    • Measure the specific gravity every hour. Discontinue the equalization charge when the gravity no longer rises
    WARNING: Do not equalize gel or AGM batteries
    If these are flooded cell batteries with access (removable caps), then you should be taking specific gravity readings with a hydrometer (temperature corrected) when new (and fully charged/equalized) and once in a while (once a week/month or so) to ensure you know what state your bank is in. When problems start, take some SG readings to find high/low cells, and see if you can recharge/equalize back to a "stable" set of readings (stop equalization once SG does not move in 1 hour).

    Personally, I do not like more than 2-3 battery strings in parallel--I would prefer fewer strings in parallel with larger capacity cells. Otherwise, you run the risk of poor cabling/bad connections (or even bad batteries/cells) causing unequal charging and discharging of the battery bank.

    Some vendors say that excessive number of paralleled batteries causes issues. To be fair, our host (NAWS) has said they do not see any battery life issues with >3 strings in parallel in a properly maintained bank.

    Lastly, I highly recommend some sort of Battery Monitor for your bank--and I personally believe that if you have AGM/Sealed batteries, a Battery Monitor is almost mandatory to help ensure the bank is operated correctly.

    Note: Knowing your daily loads (by season, if appropriate) is helpful to properly sizing your battery bank. Lots of deep cycles below 50% reduces the total number of charging cycles before death.

    And very little discharging (say less than 10% per day) is sort of a waste of battery capacity and the batteries may "age" to death before they cycle to death.

    Normally, we recommend that the battery capacity be roughly 3x your daily use (3 days of "no sun") and a 50% maximum discharge--or 6x your daily capacity as a good trade-off between life and costs.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    Re: Batteries just not holding a charge

    Bill has Great links to follow up on, but keep in mind to use them as a learning tool. the fact that Trojan want you to equalize only if you have cells with a certain variation, doesn't mean thats true of your battery. As I recall, Crown and Rolls wants likes equalizing at least once every 6 months, most forklift batteries require monthly if not more often Equalizing.

    Any Battery guy who says to add new batteries to a 3+ year old string, with out telling you it's a stop gap to get you through for a year, isn't worth a dang and shouldn't be considered for any information.

    I'm using 4 - 6 volt golf cart batteries (one string 24volt setup) and they are at the end of their life, but I regularly abuse them over the summer drawing them down to 50% or less charge. I expected to get 3 years out of them and I'm happy.

    I typically expect;

    3-5 years from cheap golf cart batteries
    4-8 years out of Trojan Golf Cart/AE batteries
    5-7 years out of cheap L-16
    5-10 years out of quality L-16 Trojan, Rolls
    7+ years out of batteries built with 60+lbs cells

    I try to get the most bang for the buck even if I have to put in some work so I don't find AGM batteries cost effective for me.

    If your approaching 4.5 years out of unmaintained multiple strings of golfcart size batteries, they are pretty much at the end of their, life.even L-16's would be at the end if unmaintained, In my opinion.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former, 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.