More battery basics.

Possibly, those tenders work like that but I doubt it. It's more plausible that if the battery drops to 12.7, the tender latches relay closed or an IC channels 14 or so volts back into the battery. I don't own a tender so can't accurately speak to the actual voltage and current measured. Remember, the Tender Plus is rated at approximately 1.5 A. At that low level of current, it would be better to increase voltage above 13V or 14V to move charge to the battery. At least that is how I would design the thing, lol.

Maybe, a Forum member has measured the charge of the Tender Plus and can give the exact measurements.

westend wrote:
If your battery had a OCV voltage of 12.8V and the tender or converter was powered with an output of 12.8V, there would be no charging at all. The charging device needs to have a voltage greater than the battery.

Your converter will vary the CURRENT into the battery at a slightly greater voltage to keep the battery charged. The tender, AFAIK, operates at 1.25A with a voltage greater than the battery to keep it charged. The tender may lower the current or interrupt the charge when it senses the battery is full. It depends on how the tender is built.

FWIW, I made a small trickle charger using a wall transformer. The transformer was rated at 12V, 300mA Measured output without a load was 16V. Using the trickler with a partly discharged battery, the voltage of the battery gradually rose over three days to 14V, at which time I unplugged the charger. The next day, the OCV voltage of the battery was 12.7V. Hope this example helps.

Understood, but I was thinking that when the battery reached fully charged, 12.8 would keep 12.8 at 12.8. If your battery dropped to 12.7, 12.8 would trickle it back up to 12.8 hence multi-stage tenders.

smkettner wrote:
13.2 can be left on indefinitely even in hot 100+ temperatures.
Many older converters held 13.8 volts and that is a bit high.

The 12 Volt Side of Life

After all this battery talk I measured the voltage at the battery terminals and found 13.20 volts. Never had any battery trouble and the battery is always up. I very seldom add water and check the water level once a month. Trailer is plugged into shore power 24/7.

Thanks for fielding all the rookie questions gentlemen.

Barkoff wrote:
Is the fact that I hook up to the positive and negative terminals that the batteries feed to and accessories hook up to,l and not the batteries themselves, a problem?

no

If your battery had a OCV voltage of 12.8V and the tender or converter was powered with an output of 12.8V, there would be no charging at all. The charging device needs to have a voltage greater than the battery.

Your converter will vary the CURRENT into the battery at a slightly greater voltage to keep the battery charged. The tender, AFAIK, operates at 1.25A with a voltage greater than the battery to keep it charged. The tender may lower the current or interrupt the charge when it senses the battery is full. It depends on how the tender is built.

FWIW, I made a small trickle charger using a wall transformer. The transformer was rated at 12V, 300mA Measured output without a load was 16V. Using the trickler with a partly discharged battery, the voltage of the battery gradually rose over three days to 14V, at which time I unplugged the charger. The next day, the OCV voltage of the battery was 12.7V. Hope this example helps.

westend wrote:

Barkoff wrote:

smkettner wrote:
13.2 can be left on indefinitely even in hot 100+ temperatures.
Many older converters held 13.8 volts and that is a bit high.

The 12 Volt Side of Life

OK, so if my camper converter with the battery switch on is supplying a constant 13.2, that is OK to leave on for weeks on end?

I went through two Interstate batteries in one year doing that? I'll try it again and make sure it isn't feeding the batteries more than 13.2 0r 13.4

What voltage do you think would be correct?
I think we've already established that many owners are supplying charge continually with success.

The demise of your previous Interstate batteries may have been because you were reluctant to keep them charged. Left in a depleted state, they will sulfate and then will be going to the battery hospice.

FWIW, I have five batteries in two banks. Both banks have been charged daily with a temp compensated voltage of 14.8 V in bulk. The daily regimen, when in storage, keeps the float voltage above 13.6. I have added water twice in the last year and the wet cells have an SG of close to 1.30. It just can't get much better than that.

Well I figured once charged to fully charged say 12.8, I thought the tender would just trickle in 12.8 12.9 not 13.6

Barkoff wrote:

smkettner wrote:
13.2 can be left on indefinitely even in hot 100+ temperatures.
Many older converters held 13.8 volts and that is a bit high.

The 12 Volt Side of Life

OK, so if my camper converter with the battery switch on is supplying a constant 13.2, that is OK to leave on for weeks on end?

I went through two Interstate batteries in one year doing that? I'll try it again and make sure it isn't feeding the batteries more than 13.2 0r 13.4

What voltage do you think would be correct?
I think we've already established that many owners are supplying charge continually with success.

The demise of your previous Interstate batteries may have been because you were reluctant to keep them charged. Left in a depleted state, they will sulfate and then will be going to the battery hospice.

FWIW, I have five batteries in two banks. Both banks have been charged daily with a temp compensated voltage of 14.8 V in bulk. The daily regimen, when in storage, keeps the float voltage above 13.6. I have added water twice in the last year and the wet cells have an SG of close to 1.30. It just can't get much better than that.

Still need to check the water level. However you should not need any but every 6 to 12 months.
Yes 13.2/13.4 volts is good to go 24/7/365.

smkettner wrote:
13.2 can be left on indefinitely even in hot 100+ temperatures.
Many older converters held 13.8 volts and that is a bit high.

The 12 Volt Side of Life

OK, so if my camper converter with the battery switch on is supplying a constant 13.2, that is OK to leave on for weeks on end?

I went through two Interstate batteries in one year doing that? I'll try it again and make sure it isn't feeding the batteries more than 13.2 0r 13.4