With the age of your system and making an assumption that the converter is an original, like Steve stated, the older converters many of them of that era needed the battery to act as a large capacitor in the system to make the converter create stable 12 VDC. They have worked erratic without the battery to hold it stable.
And making some assumptions that your camper is still wired as original about the only thing that will work direct on 120VAC is the wall outlets, and the microwave if it has one. The fridge and the AC unit still used 12 VDC for the control boards even on a brand new one. The HW heater, well yours may be total gas operation I do not know with out looking up a model # on one that old. The furnace is 12 VDC so if you want heat, you need 12 volts.
So some how you have to create stable 12 VDC to make the rest of the camper to work. By adding a battery to your existing converter it will take care of the problem back to the original setup.
However, caution, the older converters where not always the best battery maintainers. While they will charge they do not maintain well when plugged in 24/7 non stop for months on end. Many have been known to cook a battery to death connected 24/7 for weeks straight as there is no float charge mode in them. They stay stuck at the 13.65 volts area and keep pumping that higher voltage into the battery. If your where using the camper like a normal hook and up go once a week or once a month camper the system is unplugged and odds are better it is not cooking your battery to death.
There are options. First is what in the world converter do you have and what voltage is it putting out once the battery reaches 100% state of charge? Do you have a volt meter?
Normal charge is in 13.65 volts DC area. Just put the volt meter on the battery terminals when the converter is plugged into shore power. It can and will takes a day or 2 to reach 100% full charge. So seeing 13.65 volts for 2 days is not a problem. However on day 3 an 4 it should be dropping down to 13.25 volts. If it does not, odds are yours does not have a trickle mode or float mode. If you have gone a week and the thing still not drop to 13.25 well then your going to cook the battery to death over a long time period as you boil out the battery.
Now if it does drop to 13.25 then well what amperage is it at? This gets a little more tricky to sort out if it is going into float mode. You need an amp meter and need to know what milliamps of current it is sending the battery. If you have an amp meter and want to drill this deep then let talk some more.
OR do this.
Install a new higher end power converter like the Progressive Dynamics brand. They can work stable with no battery. Cost is like $200. bit expensive in your case and a ton of overkill but it will work.
OR Buy a Battery Minder Plus that maintains and conditions the battery and will not kill it.
BatteryMINDer® Plus 12 Volt 1.33 Amp Charger-Maintainer-Conditioner (Desulfator) | All | Battery Chargers by BatteryMINDers.com
These are float chargers complete with a desulfation mode. A quick search on the web for that model and make turns them up for $40. Here is one fast hit, There are more places that sell them. Amazon.com: VDC Electronics BatteryMINDer Charger, Maintainer, Desulphator - 1.3 Amp, 12 Volt, Model# 12117: Automotive
So if you go this route heads up. Before plugging the Battery Minder in attached to the battery you have to unhook the converter from suppling power to the battery. Or else you have 2 charging sources going into the same battery and may toast the Battery minder. There are a few ways to do this.
- Unhook the battery cable. A pain in the neck but works.
- Install a disconnect switch on the battery wire near the battery to simply disconnect the battery.
- Shut off the circuit breaker to the converter if you still want 120 VAC in the camper.
- Pull the shore line plug and no 120AC to the camper.
The goal is, when you leave the camper to go back home, let the battery minder maintain the battery. It will be in top shape and last many many years. Will not boil out the battery, will desulfate it and it will be at 100% state of charge when you come back a week, month or year later. When you come to camp and start using a lot of 12 DC, unhook the battery minder and run the converter. No worries if you just walk in and turn on a light or 2 but running the furnace and other high usage items it cannot keep up. It is only a 1.3amp charger.
For battery choices, Wal-Mart has a deep cycle battery made by Johnson Controls most times for like $70. Or you can get the higher grade ones if you want. They low end ones have 1 year warranty. While a starter battery will work a deep cycle adds better value over the long haul in a camper situation.
Say you are at the CG and the power goes out. The deep cycle can last all weekend if you not using a lot of high power all the time. It may get drained to 40% state of charge. Then recharge it back and life is good.
The starter battery does not like those deep discharges as much. Both will work in your case but you many find it is only $10 to $20 difference between a Group 24 deep cycle and a starter battery. If you have an older starter battery just laying around, then by all means use it until it dies. Take the old one out of your truck, put a new one in the truck and then the old one on the camper. The Battery Minder Plus will bring it back to life as good as it is going to be.
Oh and the dumb question newbie thing. No worries, there are no dumb questions on Sunline Owners Club and we encourage new members. So the only foolish question is the one no one asks. Ask away.