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USMCRET · 08-15-2018, 06:54 AM

I load tested all of my batteries yesterday, and they all passed with flying colors.

All of my batteries are six years old. I have kept a steady charge on them since day one.

I'm having a couple of odd happenings that cause me to think it could be related to the age of the batteries, but the load testing suggests otherwise.

Symptoms:

1. When I pull into a CG and plug into shore power, it takes an unusually long time for the batteries to achieve fully charged status according to the Xantrex readout.

2. The house batteries seem to discharge at an accelerated rate compared to historical experience.

3. I water my batteries monthly, and they take more water than they used to. Not excessive, but more than typical.

Those symptoms tell me the batteries are either at or beyond their service life, but I'm stumbling over the load test results.

How do I reconcile this? What do you think?

bruceisla · 08-15-2018, 07:02 AM

Quote:

Originally Posted by USMCRET

I load tested all of my batteries yesterday, and they all passed with flying colors.

All of my batteries are six years old. I have kept a steady charge on them since day one.

I'm having a couple of odd happenings that cause me to think it could be related to the age of the batteries, but the load testing suggests otherwise.

Symptoms:

1. When I pull into a CG and plug into shore power, it takes an unusually long time for the batteries to achieve fully charged status according to the Xantrex readout.

2. The house batteries seem to discharge at an accelerated rate compared to historical experience.

3. I water my batteries monthly, and they take more water than they used to. Not excessive, but more than typical.

Those symptoms tell me the batteries are either at or beyond their service life, but I'm stumbling over the load test results.

How do I reconcile this? What do you think?

Are your house batteries being charged enroute via the engine alternator and BIRD system?

twinboat · 08-15-2018, 07:17 AM

A standard load tester is not a good way to check capacity of a deep cycle battery. What they check is CCA and voltage levels under a 15 second load.

A good test of capacity is to charge to100% and then apply a set load for a set time and then let them rest a few hours and recheck the voltage.

If you have a 200 AH battery, it should deliver 10 amps for 20 hours ( 10×20=200 ) before it drops to 11.58 volts or 20% of its capacity.
Here is a link that may help.

https://www.solar-electric.com/learn...ttery-faq.html

USMCRET · 08-15-2018, 09:00 AM

Quote:

Originally Posted by twinboat

A standard load tester is not a good way to check capacity of a deep cycle battery. What they check is CCA and voltage levels under a 15 second load.

A good test of capacity is to charge to100% and then apply a set load for a set time and then let them rest a few hours and recheck the voltage.

If you have a 200 AH battery, it should deliver 10 amps for 20 hours ( 10×20=200 ) before it drops to 11.58 volts or 20% of its capacity.
Here is a link that may help.

https://www.solar-electric.com/learn...ttery-faq.html

Perfect! Thanks.

Gary RVRoamer · 08-15-2018, 10:16 AM

Elaborating on what twinboat said, the standard load test will show a shorted or otherwise obviously bad battery, but gives only a vague indication of the amp-hour capacity. It's not calibrated for that at all. Voltage is still fine, and they still deliver enough amps to pass the load test. However, a 6 year old deep cycle is probably lucky to have 75-85% of its original capacity.

The increase in water usage suggests the battery is getting hotter during charging or discharging, another sign of age.

vsheetz · 08-15-2018, 10:52 AM

Basic liad test is a good way to determine a defective battery. The other indicators you mentioned are a good way to determine tired batteries that are nearing end of life. They are I my good for x number of duscharge cycles. Its time for a new battery bank. IMHO.

bucks2 · 08-15-2018, 12:09 PM

I'm a fan of the good old hydrometer. Check each cell and I bet you'll find one 10-20% lower than the rest. While a load test gives a partial answer to the battery condition question, checking the specific gravity of each cell helps define the answer. I bet you've noticed that one cell generally needs more water than the others too. That's the one that will be off on your hydrometer test. Another quick and dirty test for a bad cell is during charging after the batteries have been drawn down a ways. Use your non-contact thermometer and look for the hottest cell.