3 batteries in 3 months

Tailgate215@yahoo.com

First post here... appreciate any help or ideas.

2014 EZ-GO RXV, large tires, fast gears. 48 volt US Battery system of 4 12v VRX deep cycles.

All is fine for 2 years then fast power drops on the state of charge meter. Getting 8 miles before depleting to 1/2 or less, sluggish on small hills like never before. I could expect to deplete 1/4 or so, but 1/2 to 3/4 is troubling. And the drops were very, very quick.

Dealer has replaced in warranty 3 of the 4 batteries in last 3 months as the problem would continue after each replacement.

Today again traveled 8 miles and depleted to 1/2 on the meter. I don't know if the 4th battery needs to be replaced or not.

Has anyone run into a bad batch of batteries before? 2 years of normal usage and something else is happening now. I asked dealer on last replacement if the 4th original battery tested ok and he said they ran a load long enough to determine that there was nothing wrong with the last battery.

Thanks in advance for any ideas...

BGW

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AZ.

No, but every time you add a new battery to a pack of old, beats the daylights out of the new one!

Would we have a chart made that shows how adding one or two new batteries diminish the whole pack over time or draw?

ThreeCW

Tailgate,

Welcome to the BGW forum

Battery life is a function of how you use them and how well you maintain them.

To achieve maximum battery cycle life, you should limit your depth of discharge to 50% (or less). The deeper the discharge, the less cycles you will get from a battery. Some BGW members report getting as much as 7 years life from a set of batteries, although 4 to 5 years seems to be a more typical battery life. Other BGW member report batteries failing in as short as 1 to 2 years.

As per the attached US Battery Expected Life Cycle Chart, at an 80% depth of discharge, the battery life has been tested to be 675 cycles. Similarly, at a 50% depth of discharge, 1150 cycles are expected. And at a 20% depth of discharge, 3300 cycles are expected in the life a battery.

What is your estimated typical depth of discharge when using your batteries? If you are drawing them down until the cart can barely move, that would be a very high depth of discharge which would result in a shorter battery life.

Another factor in a battery life is how well they are maintained. Keeping correct electrolyte levels by using only distilled or de-ionized water is important ... many an battery has been weakened / killed by under watering.

Charging is also an important maintenance factor. Batteries that are deeply discharged and left uncharged will sulfate resulting in permanent damage and shorted life. Good charging practices include limiting the depth of discharge to a low as practical and recharging your batteries as soon as possible after using your cart.

I have also attached a State of Charge Chart for your reference ... although measuring each batteries stabilized voltage is not a 100% accurate way of determining Depth of Discharge, it is usually much more accurate than using bar meters showing state of charge.

It would be helpful to find out about your battery usage patterns and maintenance practices to help you troubleshoot your problem.

I also agree with AZ that having one weak battery in a battery pack will result in a weak pack. Like a chain that is only as strong as its weakest link, a battery pack is only as strong as its weakest battery.

Regards, 3CW

Attached Images

	US Battery Expected Average Cycles Chart.JPG (138.1 KB, 0 views)
	Carts Unlimited State of Charge Chart.JPG (71.0 KB, 0 views)

JohnnieB

I don't have a chart, nor do I have the empirical data to make one, but I have an explanation that applies to both mixing old and new batteries as well as tapping the pack for 12V accessories.

The batteries in a golf cart battery pack are connected in series are charged and discharged from the two ends of the series circuit. If all of the batteries have the same storage capacity, all will give up the same amount of stored energy upon discharge and the same amount of energy will be returned to each battery upon charge. Since the charger only sees the average on-charge voltage of all the batteries in the battery pack, if they are not equal in storage capacity, the batteries with less storage capacity will reach full charge first and will be overcharged while the other batteries do not receive a full charge and chronic overcharging and undercharging kills batteries.

The first attachment shows how storage capacity varies over a lead-acid battery's lifetime. If a battery dies, it can be replaced with a used battery that is about the same age and has about the same number of charge cycles as the others without major trauma, but other than that, you are dicing with hard-earned dollars.

Technically, a lead-acid battery isn't fully charged until the on-charge voltage stops rising and many of the modern chargers us dV/dT (change in Voltage over change in Time) technology to determine when to end the charge cycle, while the legacy chargers shut of at a predetermined voltage, so the modern chargers charge the battery pack more fully, but they still only see the average of all the batteries in the pack and the problem still exists. The only way to avoid such problems (other than not mixing old and new batteries or not tapping the pack for 12V accessories) is charge in parallel. In other words, have a separate charger for each battery in the pack, but that would be a very complex charging system to say the least.

FWIW: Also attached is a composite of the charge cycles vs SoC for four popular battery brands. More correctly, the only four I could find the data on.

Attached Images

	cycle-life-lead-acid.jpg (21.5 KB, 0 views)
	SoC vs Lifespan.jpg (127.8 KB, 0 views)

JohnnieB

The question is, how does the load testing of the old battery compare to the new batteries? If they aren't the same, or very similar, there is a problem.


With taller than stock tires and fast gears, using six 8v batteries rather than four 12V batteries is definitely an upgrade to think about.