Battery Tenders

[Daddy_Bear]

I have two new RV Batteries and want to keep them completely charged. Stupid question I know, but here goes. What size battery tender do I need to get and can I just hook it to one of the batteries in order to charge both of them. They are wired together. Does anyone have recommendations?

Thanks

[Sam_Spade]

Daddy Bear wrote:
So I want to take better care from the start with these two new batteries.

The first thing you need to do is get a little multi-meter so that you can read the actual voltages instead of guessing at things.

You can get a pretty good one at WalMart or Lowes etc. for $20 or less. You can get one from Harbor Freight that is adequate for about $7....or less on sale.

Edit: I see that you have that covered so......it is possible that they gave you the batteries in a discharged state and it might take several days of continuous charge to bring them up to near full.
Leave them on charge for about 3 days; then leave the battery switch ON with the charging off for 24 hours and see what the voltage is.

If this is a brand new unit and they gave you batteries that had been sitting around in a discharged state for months on end, they might be shot already.

[Daddy_Bear]

Here's another tidbit of info. I checked the voltage last evening once with the shore power connected and got 14 volts and once w/O shore power connected and they bounced b/t 13 & 14 volts. I didn't leave the shore power disconnected long enough to see if the CO detector set off an alarm or not. Will do that this evening.

We are heading out on a one week trip to the Oregon coast next week and don't to deal with an alarm that I cant shut off if we are on batter power.

[Kit_Carson]

Bobbo wrote:
Depends on the draw. You need to get one big enough to cover all parasitic draws plus about 5 amps.

Hook the positive cable to one battery, and the negative cable to the other battery.

This what I did but I disconnected the main negative cable from the battery before installing the battery tender. When I exercise my generator or get ready for a trip, I connect the negative cable back to the battery. Has worked for me for about 2 years now.

[Daddy_Bear]

Beemerphile1 wrote:
Tell us the brand and model number of the converter in your Grand Design and we will tell you what it does.

I don't know right off what brand the converter is. I will look through the paperwork this evening. Here's what started the whole idea that I need a battery maintainer/tender.

We brought the new TH home last weekend. supposedly equipped with two new RV batteries. When I parked it in our yard and disconnected it from the tk it was late and we went to bed. The next am I went out to find the CO alarm was going off and would not reset. After looking up the flashing/beeping code it said the alarm was due to LOW Voltage. I hooked up shore power and the alarm silenced itself. The TH has been attached to shore power since. The TH does have a battery disconnect switch, but it was in the ON position.

Why would two brand new RV batteries not have enough voltage to run a CO detector? All of our other fifth wheel and trailers have had converters that was suppose to keep the batteries at full charge, but I have found over the years that that's not always the case. So I want to take better care from the start with these two new batteries.

[Sam_Spade]

Bobbo wrote:
Only, you hook them to the terminals that are NOT wired together.

My 2007 Winnebago came with a cheap Magnatek 7345 single stage converter that always put out about 13.5 volts. It was a battery killer. After about 3 years, I junked it and bought a good 3 stage converter, a PD4655V.

You added information. The original statement by itself is NOT true because you can attach to the wrong terminals.

What brand is the 4655 ? And was it "plug and play" or was some modification necessary to get a good fit ??

[Sam_Spade]

Kayteg1 wrote:

"Float circuit" will adjust the amperage without voltage jumps.

Highly unlikely.
Unless the resistance changes, you cannot change the current without also changing the voltage.

[beemerphile1]

Daddy Bear wrote:
Thanks for all the suggestions. I need to spend some time learning some more about inverters with chargers I think.

Tell us the brand and model number of the converter in your Grand Design and we will tell you what it does.

[MEXICOWANDERER]

Just because a person does not actually see a converter's voltage change it certainly does not mean that it really isn't a poorly designed bottom-of-the-barrel "Smart" charger.

The WFCO sitting under my bed does indeed switch to 14.7 volts charge rate if the Lifeline depletes to 12.5 volts. It is utterly convinced 14.7 volts really is the factory rated 14.4 volts and the 13.75 volt mid charge is the factory rated 14.4 And the 13.2 float setting must be a waste of time.

Better yet, as temperatures slide downward into the 51 degree range, voltage slumps .15 volt. That is one finely crafted piece of cra...

...ftsmanship.

I find mentoring it, amusing.

[Bobbo]

Sam Spade wrote:
The advice of connect one lead to one battery and the other lead to the other battery only works in a parallel arrangement.

That is not right.

If the batteries are 6v wired in series, you MUST hook the positive to one battery, and the negative to the other battery. Only, you hook them to the terminals that are NOT wired together.

If the batteries are 12v wired in parallel, it does not make a huge difference how you hook the wires as long as the positive is to one of the positive terminals and the negative is to one of the negative terminals. It is only a little more efficient if they are to separate batteries.

BillyW wrote:
I have yet to see a mainstream RV as new as the OPs that doesn't have some kind of multistage charger. Mine is a bottom of the barrel 04 model and has a 3 stage WFCO charger which maintains the batteries nicely.

My 2007 Winnebago came with a cheap Magnatek 7345 single stage converter that always put out about 13.5 volts. It was a battery killer. After about 3 years, I junked it and bought a good 3 stage converter, a PD4655V.

[westend]

I vote for solar but I know it doesn't fit the bill for everyone. If the RV has parasitic draws, the first installation should be a disconnect switch, IMO. With the batteries disconnected from any draw, flooded batteries can be left alone for a month or so, depending on temps. AGM batteries can be left alone for much longer.

[Daddy_Bear]

Thanks for all the suggestions. I need to spend some time learning some more about inverters with chargers I think.

[time2roll]

The small Battery Tender brand charger is fine as long as you charge the batteries first. Otherwise the charger will time out the boost mode in about three days and just float them.

[jake2250]

Genius 3500
Heres what I use on my 2-6v golf cart batteries.

[Clay_L]

The BatteryMinder mentioned above will handle up to 4 batteries at once connected in parallel. The float voltage it provides is 13.2 v.
I used the same one on my motor homes for 12 full timing years and it did a great job. When we inherited a 3000 tree commercial orchard in CO, I bought one for the farm equipment stored for the winter. Did a great job there also.

[Kayteg1]

Multi-stage should be a red flag here.
"Float circuit" will adjust the amperage without voltage jumps.
That said my 2004 converter in Fleetwood has no stages, but will keep battery at 14V, what would destroy it if I leave it for off-season.