i have the parallax 7300 converter, two 1 y/o kirkland group 78 batteries (one house that is almost never used but to start genset, and one chassis).after a long day of charging 6 days back with batteries reading 12.78 when done, i took readings each day as charge dropped to 12.65, 12.60, and sorta hung out at 12.56 house, 12.52 chassis.charged them again for 12 hours w/ no other house things on. readings start out as 13.3 house, 13.0 chassis and at end of day, both read 13.78 w/parallax on, and 12.75 when off.12 hours later, house is 12.66 and chassis is 12.70. i predict they will be near 12.56 house and 12.50 chassis in a week.house disconnect always off if not charging. i have the BIRD that links both batts during charge.i feel batteries are maybe at 85% after a year of monthly, and some bimonthly chargings. i am curious about the parallax voltage and amperage scheme applied over the 12 hours.juat a few concerns...i wonder about the state of batts, and what charging scheme i ought to consider in future.your assessments, please.

It's going to take longer than 12 hours to fully charge your batteries with your converter. I usually plug the batteries in for a few days when we get home, A day long top off charge once a month and then a few days before we go out. At this point your batteries may need some care to get them back up.

Hate to say this but that is a terrible converter/charger. It's charging profile is terrible and the only time it isn't under charging it's over charging.I swapped mine out while it was still perfectly healthy for a Progressive Dynamics because of the superior charging and storage ability.

It sounds like you have regular wet cell batteries (batteries with liquid acid in them) in your RV.The voltage level coming from the stock Parallax 73XX converter in your RV once it has fully charged your batteries - if you then continue to leave your converter connected to the batteries - is too high of a level to be kept on regular wet cell batteries continuously. However, the voltage level coming from your converter will bring them up to full charge whenever they are low - but just take longer than other types of equipment designed to put out a higher voltage level for faster charging. Many RV owners replace the stock converters that come in their RVs so that the resulting voltages from their new chargers are better suited to their wet cell batteries for both long term storage and faster charging.All the above being said, there are different models of dry cell RV batteries available that do much better with stock RV converters. We have those kind in our RV and they are many years old with still most of their capacity left. Our RV sits in the back yard when we're not using it and with our model of dry batteries, the converter can be connected to them almost continuously without damaging them. Hence our batteries are always in full charge whenever we start out on a trip. Our batteries also charge faster than regular batteries, so the converter brings them up to around 90 % of full with only a few hours on our small quiet generator when charging in a campsite. When traveling between campsites, the main engine alternator (our RV is a motorhome) will bring our batteries up to full charge in 4-5 hours of travel time.RV converters are not always worthless, even for camping without hookups ... as they do play well with certain types of batteries.

Costco group 78 is a deep cycle? I think you are better to just leave it plugged in. Best would be a PD4645 replacement converter charging at 14.4, 13.6 then float at 13.2 volts.

What smkettner recommended above - PD4645 - would be an excellent three-stage battery charger for you to use on your wet cell RV batteries.I'm not sure, but I think that you may be able to remove your converter and install the PD4645 charger in the same place as to where your converter was installed. The PD experts here can probably explain how to do this.

opinion - costco gr 78 batts & parallax 7300 charge data

pconroy328
Explorer
May 20, 2015
burlmart wrote:

ls there an easy to read, pretty simple meter that would give me amp readings and some reliable indication of the state-of-charge of a battery?

You didn't say accurate or precise but I'm guessing that's what oyu mean by reliable. Accurate meters will be expensive, because it takes some extra work to ensure their accuracy.

Then there's periodic calibrations.

What I've found is that my *in*accurate meters are precise. They're consistent. So with a borrowed Fluke (that I trust to be accurate) I now know my Harbor Freight meter reads consistently 0.2V low and do the math in my head.
burlmart
Explorer
May 20, 2015
i think the walmart tender is schumacher. they also have a battery tester for $35, but i am not sure how to use it, especially w/ the 'entanglement' posed by the BIRD.

i guess i would put the tender on either battery, 'cuz they will both start charging and somehow share the 1.5 amp trickle.

what intrigued me was how i stumbled onto this

burlmart wrote:

with house batt ground terminal off, crank engine, turn house toggle to ON, and engine lights up house things.

this seems to say you do not need a house battery at all.
loneryder
Explorer
May 20, 2015
A simple answer would be to get a new battery tender from WalMart for $20. It's the same one everybody else sells for around $50. It trickle charges at 1.5 amp and then monitors the battery. The new ones are much better with circuits to monitor the battery and not overcharge. I have several and keep them plugged in all the time. Use them on motorcycle, mowers and motorhome.
burlmart
Explorer
May 20, 2015
smkettner wrote:

Since you are always plugged in I would not change a thing. Do keep the batteries charged when not in use.

many thanks to all who have posted, and a big apology for my confused posts. i just cannot seem to get consistent and/or expected voltages from the two 'separate' batts (house and chassis), and i know it has been an issue probably from day one. my gut says my inconsistent changes in voltage readings is all about the B.I.R.D., and if i knew where mine is, i think i would change it.

but along the lines of smketter's comment, everything pretty much works as it should, and adopting a routine of more frequent and longer shore charging while not in use seems like a practical plan.

thanks again to you all - i truly value ypur help (and patience).
burlmart
Explorer
May 17, 2015
with house disconnect toggled to STORE (OFF), i disconnect house batt's ground wire and read 12.8v between wire and battery ground terminal. is this proper? shouldn't there be no voltage?

edit

with house batt ground terminal off, crank engine, turn house toggle to ON, and engine lights up house things.

wondering if emergency solenoid is sticking, i crank engine toggling ES on dash, and no longer read voltage between house batt grund terminal and ground cable... but, not sure if some BIRD time delay is the cause.
burlmart
Explorer
May 17, 2015
i feel that maybe i am seriously handicapping my novice-level electricity monitoring with my pocket multimeter from radio shack

which a former electrician adult student recommended 15 years back in my teaching days. i also have an old banged-up-a-bit exide trickle charger and a walmart everstart 50/10/2 amp charger. i got these to monitor our small old 40 hp outboard dual cycle boat battery. (now with a sole 5.5 y/o walmart everstart happily reating at 12.7 v w/ only monthly 4 hr trickle-ups).

ls there an easy to read, pretty simple meter that would give me amp readings and some reliable indication of the state-of-charge of a battery? maybe load test too? simple and easy to see are important.
tenbear
Explorer
May 16, 2015
One of the reasons the battery voltage is high after charging and then drops is due to surface charge. The battery voltage you should be interested in is the voltage after the surface charge has leaked off. It could take hours to leak off when there is no load on the battery. A fully charged battery should be 12.6 to 12.7v after the surface charge has gone.
time2roll
Nomad
May 16, 2015
Having extra CCA will not hurt a thing. That battery is probably fine for your use. It will cycle a few times if needed but will lose capacity if done frequently.

Since you are always plugged in I would not change a thing. Do keep the batteries charged when not in use.
burlmart
Explorer
May 16, 2015
quote from OP: "charged both batts for 12 hours (all day thursday 5/14). readings start out as 13.3 house, 13.0 chassis and at end of day, both read 13.78 w/parallax on, and 12.75 when off.
12 hours later, house is 12.66 and chassis is 12.70. i predict they will be near 12.56 house and 12.50 chassis in a week."

now, 24 hours later, house 12.76, chassis 12.48. i guessed right, but chassis batt did not wait a week to drop to 12.5.

i then turn house disconnect ON, and bam, both house and chassis are 12.76!? i will leave it ON for a day or more and monitor.

cranked engine up, and alternator reads 15.15 in both batts, and drops to 14.7 in a few minutes.

i have often seen this 12.5 chassis reading and been bothered by it.
pnichols
Explorer II
May 16, 2015
burlmart wrote:
... and i keep wondering how many stages does the alternator have? i never hear it mentioned.

The Ford alternator in our motorhome seems to have "infinite" stages. This behavior is probably at least partially dependent on temperature of, or around, the alternator, but maybe not entirely ... there may be some electronics involved in controlling modern alternators' terminal voltages with other parameters being brought into play by these electronic controls.

For instance, our motorhome's 130 amp Ford alternator often starts out at around 14.4 volts but gradually drops down in voltage as we travel, which kindof is a good fit for what our coach batteries need. In scorching heat, I've seen alternator voltages as low as around 12.9 volts being applied to the coach batteries - which is exactly what I would want on their terminals from a charger during high heat.

I can see what's happening as we drive down the road or idle the main engine, as we have both an ammeter and a voltmeter right on dash that monitor the coach batteries.

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opinion - costco gr 78 batts & parallax 7300 charge data

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