Batteries just not holding a charge

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
www.batteryfaq.org

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:

Dave Sparks wrote: »

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.

-Bill