so I have 2 different pairs of 6 volt batteries on my toyhauler. one set from Costco, the golf cart bats, with a date on them of 4/12. they had been sitting in my garage for about a year-year and a half on a battery tender jr. , with it showing greenthe other pair came with the toyhauler, they are 2 6 volt agm batts, owner said they were still good and they seem like it but,,,,when I charge both pairs of batts to full charge, 13.5 or 13.6, as soon as I put a real load on them (like pulling 7 amps thru the xantrax 1800 inverter), the digital volt meter from the xantrax readout shows down to 11.1 volts, if I put a small load on them, like the heater fan, the volts fall from 13.5 to 12.5 or 12.4. from what I understand, going down to 12.3 volts, you have essentially used 40-50% of the battery capacity?my question is, are these batteries toast? obviously, each one of the pair of 6 volt batts should have at least 200 amp hours, so total 400 amp hours? and the volts drop pretty quickly, I would have assumed if I pulled 7 amps on the inverter, I should get at least 25 hours hours before I hit 12.5 volts (50% discharged). (200 amp hours divided by 8 amp load = 25 hoursany response is appreciated ( I am unsure of the date of manufacture of the agm's)Moved to Tech Issues forum from DIY.

If you have four 200 AH 6v batteries, your total capacity will be 400AH. Total usable or reasonable capacity would be around 200AH. It still doesn't explain the sudden voltage drop with using the Xantrex. If it's possible, I'd suggest to remove one pair of batteries from the circuit to the Xantrex and try that. It may be that you have one bad battery or even one bad cell in a battery.Your math is wrong on the current draw, too, if I'm understanding you correctly. If you draw 7 amps at 120V, the draw from your batteries will be in the order of 70 amps at 12VDC. At that level of draw, you would be at 50% of battery capacity within 3 hrs.

thank you, I just saw that capacity was 200 for each pair, but not getting the 7 amps to 70 amps vdc but I am sure you are right. I actually have isolated each "pair" and they both do the same thing.am I correct in assuming that going below 12.3 volts is less than 50%?

What size of battery cables are you using to connect the batteries to the LOAD.70AMPS DC current is a pretty heavy draw fro the batteries.Roy Ken

Your likely not starting with fully charged batteries. Taking the bank to 13.6 is nowhere near fully charged from a discharged state. You need to hold those batteries at 14.8 volts for at least 2 hours and that would likely get to 95%+ full.Also pulling around 70 amps DC (7 amps AC through inverter) is going to cause battery voltage to dip pretty low. That's a significant power draw. I would fully expect battery voltage to drop well below 12.0 volts with several minutes at that power draw. Under ant significant power draw, battery voltage is not a good indicator of charge state. Battery voltage charge state estimates is only good at zero draw on the battery

well, that is interesting. I have a xantrex true charge 40 (microprocessor controlled) and it brings the batts up to 13.4 and keeps them there(green ready light is on). if I shut it off, the volts drop to 13.3if it will only trickle charge at 13.4 volts, how do I get them up to 14.8 volts

6 volt battery issue question about load | Good Sam Community

16 Replies

rockwind1
Explorer II
May 11, 2014
to answer roy, the cables going to the inverter are HUGE ( realize this is an subjective term but there is no way they are too small), then of course it is just romex going from inverter to breaker panel, 14/2 with ground it appears. to load test the bats, I was plugging in some halogen flood lights I have to an outlet on the circuit that the inverter supplies.
rockwind1
Explorer II
May 11, 2014
well, that is interesting. I have a xantrex true charge 40 (microprocessor controlled) and it brings the batts up to 13.4 and keeps them there(green ready light is on). if I shut it off, the volts drop to 13.3

if it will only trickle charge at 13.4 volts, how do I get them up to 14.8 volts
hmknightnc
Explorer
May 11, 2014
Your likely not starting with fully charged batteries. Taking the bank to 13.6 is nowhere near fully charged from a discharged state. You need to hold those batteries at 14.8 volts for at least 2 hours and that would likely get to 95%+ full.

Also pulling around 70 amps DC (7 amps AC through inverter) is going to cause battery voltage to dip pretty low. That's a significant power draw. I would fully expect battery voltage to drop well below 12.0 volts with several minutes at that power draw. Under ant significant power draw, battery voltage is not a good indicator of charge state. Battery voltage charge state estimates is only good at zero draw on the battery
RoyB
Explorer II
May 11, 2014
What size of battery cables are you using to connect the batteries to the LOAD.

70AMPS DC current is a pretty heavy draw fro the batteries.

Roy Ken
rockwind1
Explorer II
May 11, 2014
thank you, I just saw that capacity was 200 for each pair, but not getting the 7 amps to 70 amps vdc but I am sure you are right. I actually have isolated each "pair" and they both do the same thing.

am I correct in assuming that going below 12.3 volts is less than 50%?
westend
Explorer
May 11, 2014
If you have four 200 AH 6v batteries, your total capacity will be 400AH. Total usable or reasonable capacity would be around 200AH. It still doesn't explain the sudden voltage drop with using the Xantrex. If it's possible, I'd suggest to remove one pair of batteries from the circuit to the Xantrex and try that. It may be that you have one bad battery or even one bad cell in a battery.

Your math is wrong on the current draw, too, if I'm understanding you correctly. If you draw 7 amps at 120V, the draw from your batteries will be in the order of 70 amps at 12VDC. At that level of draw, you would be at 50% of battery capacity within 3 hrs.

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6 volt battery issue question about load

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